Introduce Extract to Code Behind

[noahbkim]

In order to support code action efficiently, this PR's main purpose is to integrate an additional dispatcher into the RZLS framework. Additionally, it contains a 'plugin' of sorts to this framework that handles extracting @code blocks from .razor files into backing C#.

I merged with master preemptively to double check compatibility, so please ignore diffs from that.

This PR registers two endpoints with the RZLS. The first is the CodeActionEndpoint, which is a part of the O# specifications. This endpoint asks all of its registered providers (right now there is only one for ExtractToCodeBehind, but in general they are dynamically registered as RazorCodeActionProvider services) if they have any code actions to provide. All providers that apply return a command for razor/runCodeAction with params for a custom endpoint.

If the user chooses any of the code actions provided this way, the razor/runCodeAction is executed by VSCode and a new query is sent to the language server to "resolve" or compute the full set of changes invoked by the aforementioned params. This is handled by the CodeActionResolutionEndpoint, which passes the data in the params to a correspondingly registered RazorCodeActionResolver based on a shared Action constant. This returns a serialized WorkspaceEdit, which is applied on the client side.

Addresses dotnet/aspnetcore#22239 (in this specific format)

[dnfadmin]

All CLA requirements met.

[NTaylorMullen]

Wow i'm surprised that for Draft PRs it runs checks. Interesting!

[noahbkim]

I switched it to a draft after publishing because I didn't see the option first 😅

[NTaylorMullen]

Overall design looks great! Left a few high level comments. Let us know once you're ready for a more in-depth review 😄

[ajaybhargavb]

Wow i'm surprised that for Draft PRs it runs checks. Interesting!

It has always been that way. It's super useful for investigating flaky tests on the CI.

[ryanbrandenburg]

Mostly just nit-picks and stuff that probably gets cleaned up before you leave draft anyway, nothing foundational.

[ryanbrandenburg]

Pretty much all of my comments are code-style nitpicks. The bones of the code look solid.

[ajaybhargavb]

Looks really good. I had a few question and mostly minor style comments.

[CyrusNajmabadi]

Suggested change

	private static readonly Range StartOfDocumentRange = new Range(new Position(0, 0), new Position(0, 0));
	private static readonly Range StartOfDocumentRange = default;

?

[TanayParikh]

Looks great! 👏

Just some minor comments / changes / formatting.

[NTaylorMullen]

Only minor comments. Looks super good Noah!

[ryanbrandenburg]

This is still approved by me, but let me know before you merge this. I'm doing a VS insertion and I'm told this PR can't go in with that.

[ajaybhargavb]

Looks great 🎉 🍾 . Just minor nits and one question for my own understanding.