introduce test_globs field for go_package to identify test files

[tdyas]

The current design for the Go plugin has go_package own all Go sources in a directory. It is still necessary to exclude test files, however, when building a go_binary.

This PR introduces the test_globs field for go_package as the way for the Go plugin to identify which files in a go_package are test files. It defaults to ("_*test.go",) which should match the go tooling. It is a field versus hard-coded to let users override if necessary.

[ci skip-rust]

[ci skip-build-wheels]

[tdyas]

If the need to override proves unnecessary, then this could be hard-coded at a later time. I am concerned about what to do with resource files versus Go sources files that may or may not to be in a test package. For now, this is fine, and still allows me some measure of control during prototyping without introducing a go_tests target.

[benjyw]

The current design for the Go plugin has go_package own all Go sources in a directory. It is still necessary to exclude test files, however, when building a go_binary.

Can you clarify why this is necessary? Doesn't the go tooling take care of this already?

[tdyas]

Seems so. I wrote this PR earlier today before I wrote #12429 and learned the package metadata lists the regular and test files. We should probably just rely on that analysis by the go tooling.

I'll make this PR just remove the test file exclusion and just have GoSources owns all Go files in the directory.

[benjyw]

Makes sense. The more we work idiomatically with the go command the better. Since it knows to exclude test files from binaries, we should just rely on that :)

[benjyw]

It seems like the test files can be said to belong to the package, in go idiom, so...

[tdyas]

Closing in favor of just taking care of this in #12429.