Avoid accessing Document from formatter services

[tmat]

Formatting services have async methods that are asynchronous only because they need to retrieve SourceText and SyntaxTree. Some callers of the services are truly async (e.g. code fixes), but others (e.g. typing command handler) are synchronous and running on UI thread. This creates potential for undesirable scheduling of parser execution and blocking of the UI thread in the latter case.

Instead of passing Document to various formatting services and then retrieving SourceText and SyntaxTree asynchronously in these services, retrieve the text and tree upfront and make the formatting services synchronous. The text and the syntax root are packaged in DocumentSyntax struct to simplify passing them both along.

Unlike SyntacticDocument the ParsedDocument struct does not have a reference to Document. This makes the formatting code completely independent of solution snapshot and prevents from potential accidental async reads of data from Document. If in future we end up removing Solution snapshot from in-proc this approach will also allow us to keep the synchronous formatter calls in-proc as long as we have the text and trees in-proc.

Contributes to #57554

Follow ups:

• Apply this pattern for brace completion and other blocking command handlers
• Avoid reading options asynchronously when they are available from the editor buffer
• Consider replacing SyntacticDocument, doc difference from ParsedDocument if we keep it

[tmat]

Moved from DocumentExtensions

[tmat]

Moved to FormattingRuleUtilities