feat: reuse collection types for DocFitter

[TimothyMakkison]

Instead of creating a new instance of StringBuilder and Stack<PrintCommand> every time DocFitter.Fit is called we instead create a single instance of each in DocPrinter and pass it into DocFitter.Fit.

This could be replaced by using ValueStringBuilder and ValueListBuilder, the latter would be beneficial as unlike Stack<T> we can access items by index instead of the O(n) lookup time with ElementAt.

Before

Method	Mean	Error	StdDev	Median	Gen0	Gen1	Gen2	Allocated
Default_CodeFormatter	231.5 ms	4.62 ms	8.78 ms	228.0 ms	11000.0000	4000.0000	1000.0000	95.82 MB

After

Method	Mean	Error	StdDev	Gen0	Gen1	Gen2	Allocated
Default_CodeFormatter	227.0 ms	4.51 ms	6.33 ms	10000.0000	4000.0000	1000.0000	90.03 MB