perf: prevent closure creation in Modifier

[TimothyMakkison]

• Use Func<IReadOnlyList<SyntaxToken>, PrintingContext, Doc> to prevent closure formation.
• Replace Array.IndexOf with a switch expression
• Pass Comparison<SyntaxToken> to Array,Sort to prevent delegate creation each time.

I did experiment with a Doc.Join overload that takes a collection, a Func<TElement, PrintingContext, Doc> and PrintingContext, it did save 1.2MB but it is ugly as sin and awkward to use.

Benchmark (Timing is inaccurate)

Before

Method	Mean	Error	StdDev	Gen0	Gen1	Allocated
Default_CodeFormatter_Tests	222.8 ms	17.65 ms	51.50 ms	3000.0000	1000.0000	34.58 MB
Default_CodeFormatter_Complex	360.0 ms	11.02 ms	31.79 ms	5000.0000	2000.0000	53 MB

After

Method	Mean	Error	StdDev	Median	Gen0	Gen1	Allocated
Default_CodeFormatter_Tests	137.5 ms	4.25 ms	12.00 ms	133.6 ms	3000.0000	1000.0000	34.54 MB
Default_CodeFormatter_Complex	268.2 ms	5.26 ms	13.57 ms	263.0 ms	5000.0000	2000.0000	52.6 MB