Cohosting OnAutoInsert endpoint

[alexgav]

Summary of the changes

• Cohosting endpoint for auto-insert endpoint.

Fixes:
Part of #9519

Notes:

All auto-insert scenarios should be addressed now (Razor, HTML, C#)
Tests will be added in a separate PR since this one has grown large and long enough as it is.

[davidwengier]

Isn't there some mapping that needs to happen, to get the LinePositionSpan contained in this response back to Razor coordinates?

[alexgav]

Yes unfortunately. It's done in the original endpoint by the RazorFormattingService. I didn't realize that besides doing code formatting it also remaps document positions from C# to Razor (during CSharpOnTypeFormattingPass from what I can tell).

Does it mean that we need to move RazorFormattingService to the common layer after all?

[davidwengier]

Ahh yeah, I forgot that on type formatting (which this would use internally) works on being given a set of C# edits. Yes, this will need the formatting service to move down.

[davidwengier]

Happened to be looking at the existing AutoInsert endpoint today, for other reasons, and noticed is uses this: https://github.com/dotnet/razor/blob/main/src/Razor/src/Microsoft.AspNetCore.Razor.LanguageServer/AutoInsert/PreferHtmlInAttributeValuesDocumentPositionStrategy.cs#L19

We'll need to do that here too, to get matching behaviour. Should be able to just move it down to Workspaces, and call the static Instance property etc.