perf: use ValueListBuilder for BaseMethodDeclaration

[TimothyMakkison]

Replace List<Doc> with ValueListBuilder<Doc>

Benchmark (timing is inaccurate)

Before

Method	Mean	Error	StdDev	Gen0	Gen1	Allocated
Default_CodeFormatter_Tests	154.7 ms	3.06 ms	6.98 ms	3000.0000	1000.0000	35.16 MB
Default_CodeFormatter_Complex	337.9 ms	9.81 ms	28.93 ms	5000.0000	2000.0000	54.8 MB

After

Method	Mean	Error	StdDev	Gen0	Gen1	Allocated
Default_CodeFormatter_Tests	131.1 ms	2.59 ms	4.79 ms	3000.0000	1000.0000	34.52 MB
Default_CodeFormatter_Complex	261.1 ms	5.16 ms	5.07 ms	5000.0000	2000.0000	52.37 MB