test: re-order slow API tests

[erickzhao]

api.slow.spec.ts is the slowest test suite that we have, but is the set of integration tests that test our Forge commands end-to-end.

This PR does a few things to clean up the implementation of this suite:

• Removes the beforeInitTest helper in favour of directly calling api.init in our tests. This makes the tests a bit easier to read.
• Re-orders describe and it blocks to better represent the hierarchy of tests.
• Avoids dynamically calling it in loops to create tests for Makers. Instead, leverage describe.each and it.each.
• Removes the process.env.DISABLE_SQUIRREL_TEST environment variable from the MakerSquirrel implementation code, which we were using to disable the maker in tests.

 ✓  slow  packages/api/core/spec/slow/api.slow.spec.ts (66 tests) 418819ms
   ✓ with package manager = 'npm' > import > creates forge.config.js and can successfully package the application 15300ms
   ✓ with package manager = 'npm' > init > should successfully initialize a Forge project 12011ms
   ✓ with package manager = 'npm' > init > when directory already exists > should fail by default
   ✓ with package manager = 'npm' > init > when directory already exists > should successfully initialize if --force flag is on 11617ms
   ✓ with package manager = 'npm' > init > with skipGit > should not initialize a git repo if passed the skipGit option 11941ms
   ✓ with package manager = 'npm' > init > with custom templates > writes custom files correctly 13095ms
   ✓ with package manager = 'npm' > init > with custom templates > fails if template does not specify a Forge version
   ✓ with package manager = 'npm' > init > with custom templates > fails if template has a mismatched Forge version
   ✓ with package manager = 'npm' > init > with custom templates > fail if template does not exist
   ✓ with package manager = 'npm' > after init > package > throws an error when packagerConfig.all is set
   ✓ with package manager = 'npm' > after init > package > can package without errors 1626ms
   ✓ with package manager = 'npm' > after init > package > with custom outDir > should package to custom directory 1571ms
   ✓ with package manager = 'npm' > after init > package > with custom outDir > can make from custom directory 8327ms
   ✓ with package manager = 'npm' > after init > package > with prebuilt native module deps installed > should succeed 5342ms
   ✓ with package manager = 'npm' > after init > make > for target MakerDMG.js > can make without errors 7982ms
   ✓ with package manager = 'npm' > after init > make > for target MakerZIP.js > can make without errors 8461ms
   ✓ with package manager = 'npm' > after init > make > for target MakerSnap.js > fails
   ✓ with package manager = 'npm' > after init > make > throws an error when given an unrecognized platform
   ✓ with package manager = 'npm' > after init > make > throws an error when the specified maker doesn't support the current platform
   ✓ with package manager = 'npm' > after init > make > throws an error when the specified maker doesn't implement isSupportedOnCurrentPlatform()
   ✓ with package manager = 'npm' > after init > make > throws an error when no makers are configured for the given platform
   ✓ with package manager = 'npm' > after init > make > can make for the MAS platform successfully 12305ms
   ✓ with package manager = 'yarn' > import > creates forge.config.js and can successfully package the application 13890ms
   ✓ with package manager = 'yarn' > init > should successfully initialize a Forge project 12201ms
   ✓ with package manager = 'yarn' > init > when directory already exists > should fail by default
   ✓ with package manager = 'yarn' > init > when directory already exists > should successfully initialize if --force flag is on 12100ms
   ✓ with package manager = 'yarn' > init > with skipGit > should not initialize a git repo if passed the skipGit option 12313ms
   ✓ with package manager = 'yarn' > init > with custom templates > writes custom files correctly 13007ms
   ✓ with package manager = 'yarn' > init > with custom templates > fails if template does not specify a Forge version
   ✓ with package manager = 'yarn' > init > with custom templates > fails if template has a mismatched Forge version
   ✓ with package manager = 'yarn' > init > with custom templates > fail if template does not exist
   ✓ with package manager = 'yarn' > after init > package > throws an error when packagerConfig.all is set
   ✓ with package manager = 'yarn' > after init > package > can package without errors 1716ms
   ✓ with package manager = 'yarn' > after init > package > with custom outDir > should package to custom directory 1698ms
   ✓ with package manager = 'yarn' > after init > package > with custom outDir > can make from custom directory 8548ms
   ✓ with package manager = 'yarn' > after init > package > with prebuilt native module deps installed > should succeed 5601ms
   ✓ with package manager = 'yarn' > after init > make > for target MakerDMG.js > can make without errors 7900ms
   ✓ with package manager = 'yarn' > after init > make > for target MakerZIP.js > can make without errors 8643ms
   ✓ with package manager = 'yarn' > after init > make > for target MakerSnap.js > fails
   ✓ with package manager = 'yarn' > after init > make > throws an error when given an unrecognized platform
   ✓ with package manager = 'yarn' > after init > make > throws an error when the specified maker doesn't support the current platform
   ✓ with package manager = 'yarn' > after init > make > throws an error when the specified maker doesn't implement isSupportedOnCurrentPlatform()
   ✓ with package manager = 'yarn' > after init > make > throws an error when no makers are configured for the given platform
   ✓ with package manager = 'yarn' > after init > make > can make for the MAS platform successfully 11345ms
   ✓ with package manager = 'pnpm' > import > creates forge.config.js and can successfully package the application 14841ms
   ✓ with package manager = 'pnpm' > init > should successfully initialize a Forge project 16937ms
   ✓ with package manager = 'pnpm' > init > when directory already exists > should fail by default
   ✓ with package manager = 'pnpm' > init > when directory already exists > should successfully initialize if --force flag is on 19314ms
   ✓ with package manager = 'pnpm' > init > with skipGit > should not initialize a git repo if passed the skipGit option 12969ms
   ✓ with package manager = 'pnpm' > init > with custom templates > writes custom files correctly 13816ms
   ✓ with package manager = 'pnpm' > init > with custom templates > fails if template does not specify a Forge version
   ✓ with package manager = 'pnpm' > init > with custom templates > fails if template has a mismatched Forge version
   ✓ with package manager = 'pnpm' > init > with custom templates > fail if template does not exist
   ✓ with package manager = 'pnpm' > after init > package > throws an error when packagerConfig.all is set
   ✓ with package manager = 'pnpm' > after init > package > can package without errors 1747ms
   ✓ with package manager = 'pnpm' > after init > package > with custom outDir > should package to custom directory 1705ms
   ✓ with package manager = 'pnpm' > after init > package > with custom outDir > can make from custom directory 8611ms
   ✓ with package manager = 'pnpm' > after init > package > with prebuilt native module deps installed > should succeed 5991ms
   ✓ with package manager = 'pnpm' > after init > make > for target MakerDMG.js > can make without errors 7868ms
   ✓ with package manager = 'pnpm' > after init > make > for target MakerZIP.js > can make without errors 8510ms
   ✓ with package manager = 'pnpm' > after init > make > for target MakerSnap.js > fails
   ✓ with package manager = 'pnpm' > after init > make > throws an error when given an unrecognized platform
   ✓ with package manager = 'pnpm' > after init > make > throws an error when the specified maker doesn't support the current platform
   ✓ with package manager = 'pnpm' > after init > make > throws an error when the specified maker doesn't implement isSupportedOnCurrentPlatform()
   ✓ with package manager = 'pnpm' > after init > make > throws an error when no makers are configured for the given platform
   ✓ with package manager = 'pnpm' > after init > make > can make for the MAS platform successfully 10904ms

I also went ahead and moved a few more files around to better reflect the folder structure of the src/ folder.