New Formatting Engine Followup

[davidwengier]

• OnTypeFormattingPass still uses the old formatting engine, and recompiles Razor files multiple times.
  • It should be possible for that to use the new generated document, and therefore not have to do all of the "cleanup" work after an on-type formatting operation.
  • We'll have to allow the new document generation to track a position in the original document, and map it to the generated document. Regular source mappings won't help here
• Code actions, snippets and OnAutoInsert have to use the Razor compiler generated document, because they start with edits to that document.
  • Perhaps they could have their own formatting pass, rather than use the OnTypeFormattingPass and all of its cleanup code.

Perf:

• Avoid StringBuilder.ToString(): New Razor document formatting engine #11364 (comment)
• Capture common indentation sizes and reuse: New Razor document formatting engine #11364 (comment)