Add support for incremental analysis for method body editing scenario…

[mavasani]

…s for LSP document pull diagnostics computation path, i.e. below APIs:

roslyn/src/Features/Core/Portable/Diagnostics/IDiagnosticAnalyzerService.cs

Lines 69 to 91 in f6f1c71

	/// <summary>
	/// Try to return up to date diagnostics for the given span for the document.
	///
	/// It will return true if it was able to return all up-to-date diagnostics.
	/// otherwise, false indicating there are some missing diagnostics in the diagnostic list
	///
	/// This API will only force complete analyzers that support span based analysis, i.e. compiler analyzer and
	/// <see cref="IBuiltInAnalyzer"/>s that support <see cref="DiagnosticAnalyzerCategory.SemanticSpanAnalysis"/>.
	/// For the rest of the analyzers, it will only return diagnostics if the analyzer has already been executed.
	/// Use <see cref="GetDiagnosticsForSpanAsync(Document, TextSpan?, Func{string, bool}?, bool, bool, CodeActionRequestPriority, Func{string, IDisposable?}?, CancellationToken)"/>
	/// if you want to force complete all analyzers and get up-to-date diagnostics for all analyzers for the given span.
	/// </summary>
	Task<(ImmutableArray<DiagnosticData> diagnostics, bool upToDate)> TryGetDiagnosticsForSpanAsync(Document document, TextSpan range, Func<string, bool>? shouldIncludeDiagnostic, bool includeSuppressedDiagnostics = false, CodeActionRequestPriority priority = CodeActionRequestPriority.None, CancellationToken cancellationToken = default);
	/// <summary>
	/// Return up to date diagnostics for the given span for the document
	/// <para>
	/// This can be expensive since it is force analyzing diagnostics if it doesn't have up-to-date one yet.
	/// Predicate <paramref name="shouldIncludeDiagnostic"/> filters out analyzers from execution if
	/// none of its reported diagnostics should be included in the result.
	/// </para>
	/// </summary>
	Task<ImmutableArray<DiagnosticData>> GetDiagnosticsForSpanAsync(Document document, TextSpan? range, Func<string, bool>? shouldIncludeDiagnostic, bool includeCompilerDiagnostics, bool includeSuppressedDiagnostics = false, CodeActionRequestPriority priority = CodeActionRequestPriority.None, Func<string, IDisposable?>? addOperationScope = null, CancellationToken cancellationToken = default);

The incremental analysis is currently guarded by a feature flag.

[mavasani]

Almost all the code in this file is ported from the prior implementation of incremental method body analysis in DiagnosticIncrementalAnalyzer v1 engine.

[mavasani]

This is the only new method I have added on top of the previous implementation.

[mavasani]

This type has the meat of the incremental analysis support.

[mavasani]

This is the core logic that computes latest diagnostics using latest changed member diagnostics and cached diagnostics from document snapshot prior to member edit. Almost all the code in the method is borrowed from prior implementation. I primarily added additional location handling here as we were either dropping them or not updating the spans for those, both of them were leading to asserts.