Microsoft.CodeAnalysis.Differencing.Match.ComputeMatchForLabel performance and maintainability improvements

[ivanbasov]

The Microsoft.CodeAnalysis.Differencing.Match.ComputeMatchForLabel method attempts to approximate an O(N^2) matching algorithm with multiple passes with difference distance thresholds. It is expected that those passes are often executed within O(N). However, it is not guaranteed and, O(N^2) still happens often.

Moreover, it is observed that:

1. Passes perform the same calculations multiple times. We can fix this by saving information between passes.
2. Solving some matching issues involve maintaining the set of thresholds. See support CasePatternSwitchLabel in StatementSyntaxComparer  #18970. This looks fragile.