feat: resource-scoped configuration support

[adalinesimonian]

This is a major feature. With this support, we now support multiple workspaces opened at once in VS Code, which we've never done before. Using this, we should be also able to massively speed up e2e tests.

If the client supports the workspace/configuration request, we use it to pull extension settings per resource (e.g. document). If it doesn't, we fall back to using a global configuration.

• Added getOptions(uri) to LanguageServerContext. Returns extension options specific to the given URI. If resource-scoped configuration isn't supported by the client, returns the global options regardless of URI.
• FormatterModule now registers formatters per document instead of per language ID.
• The DidRegisterDocumentFormattingEditProvider language server notification and its corresponding extension API event now provide the URI and registration options for each registration. This is used by the formatter test to wait for the specific registration that applies to the document fixture.
• formattingReady flag removed from extension API.
• options removed from LanguageServerContext.
• onDidChangeValidateLanguages language server event removed.

[adalinesimonian]

Unit tests haven't been updated just yet, so linting and testing will not work for this PR on CI for the time being. However, end-to-end tests pass if you run them yourself, and I've manually validated functionality in a single workspace and in a multi-root workspace.

[adalinesimonian]

End-to-end tests have always been sluggish for this project. Not anymore!

With the latest commit, here are the test results on my machine:

Test Suites: 14 passed, 14 total
Tests:       17 passed, 17 total
Snapshots:   17 passed, 17 total
Time:        20.459 s

That's right — just over 20 seconds for ALL of the end-to-end tests!

And with that, I'm calling it a night. Can't wait to see what it'll be like on CI once I get the unit tests working.

[adalinesimonian]

End-to-end test run times on GitHub Actions:

• Ubuntu test runner: ~35 seconds

  Down from ~1 minute 19 seconds
  Originally ~1 minute 50 seconds before first consolidation

• Windows test runner: ~39 seconds

  Down from ~1 minute 35 seconds
  Originally ~2 minutes 15 seconds before first consolidation

• macOS test runner: ~53 seconds

  Down from ~1 minute 48 seconds
  Originally ~2 minutes 26 seconds before first consolidation

[adalinesimonian]

I'm going to merge this now; I'm working on other tasks and it would be nice not to have conflicts when creating/modifying e2e tests and also for those tests to go by much more quickly. Happy to make changes in a patch commit/PR!