Add experimental.enableProjectDiagnostics setting.

[TheCymaera]

Is your feature request related to a problem? Please describe.

TypeScript has a setting for enabling project wide diagnostics. It gives us error messages and refactoring capabilities for files that are not open in the editor.

typescript.tsserver.experimental.enableProjectDiagnostics

Describe the solution you'd like

Add an equivalent setting for Deno.

deno.tsserver.experimental.enableProjectDiagnostics

[jespertheend]

This is somewhat related to #437, though I think that issue is more about suppressing the errors from project diagnostics rather than adding a new setting.

[bobmoff]

I would love this feature! ❤️

The issue right now is that when updating something in a file I don't see the effects in other files until I run the script. Would love to be able to just see the same issues that are detected when running check on the project but inside VSCode in the problems pane.

I can setup a task in VSCode, but then I would have to remember to run that task every now and then.

[tom-sherman]

The TypeScript vscode extension provides a "tsc: watch" task that will watch the directory for changes and rerun the compiler, it has a special problem matcher to grab the output and present it in the problems pane in vscode. I use this sometimes when doing large refactors

As far as I'm aware, Deno doesn't currently have a way to do this typechecking in watch mode - does it?