perf: fast comparison using `FullSpan` and source code

[TimothyMakkison]

• Compare the old and formatted code before using SyntaxNodeComparer (ie new version of csharpier, no changes but hash is cache is invalidated)
• Skip comparison if two TypeDeclaration aka (classes, struct, interfaces etc) or MethodDeclaration are identical
  • This could be done for all SyntaxNodes but may slow things down if most nodes have changed

The CLI spends up to 30% of the time doing comparisons, with this, we can skip cases with identical source code, and only compare types/methods that have changed. The performance degradation for lots of changes (i.e. first time a project is formatted) shouldn't be that great as CompareFullSpan is basically a fast SequenceEqual and only used for type declarations and methods.