Document state storage refactoring

[tmat]

Alternative to #50298. Keeping the previous data structure: ImmutableList and ImmutableSortedDictionary.

• Refactors storage of document ids and states in ProjectState to a dedicated data structure: TextDocumentStates<TState>.
• Use TextDocumentStates<TState> for source generated documents as well.
• Improve performance of Project.Documents: 1.5-2.25x faster. Partially addresses Experiment with targetted perf improvements around Project.Documents. #48682.

Before

Method	DocumentCount	Mean	Error	StdDev	Gen 0	Gen 1	Gen 2	Allocated
Project.DocumentIds	0	24.42 ns	0.194 ns	0.181 ns	-	-	-	-
Project.Documents	0	78.83 ns	0.503 ns	0.446 ns	0.0772	-	-	128 B
Project.DocumentIds	100	8,172.07 ns	8.030 ns	7.118 ns	0.0305	-	-	72 B
Project.Documents	100	24,651.12 ns	98.105 ns	91.767 ns	0.0916	-	-	201 B
Solution.WithDocumentText	100	12,661.10 ns	252.509 ns	319.343 ns	0.8240	0.2594	-	5172 B
Project.DocumentIds	10000	859,548.56 ns	399.791 ns	373.965 ns	-	-	-	80 B
Project.Documents	10000	4,203,826.43 ns	19,733.173 ns	18,458.422 ns	-	-	-	256 B
Solution.WithDocumentText	10000	13,574.50 ns	270.030 ns	500.518 ns	0.8545	0.2289	-	5425 B

After

Method	DocumentCount	Mean	Error	StdDev	Median	Gen 0	Gen 1	Gen 2	Allocated
Project.DocumentIds	0	23.34 ns	0.494 ns	0.891 ns	22.91 ns	-	-	-	-
Project.Documents	0	77.22 ns	0.537 ns	0.502 ns	77.31 ns	0.0772	-	-	128 B
Project.DocumentIds	100	8,159.41 ns	10.113 ns	8.965 ns	8,157.79 ns	0.0305	-	-	72 B
Project.Documents	100	16,356.60 ns	97.365 ns	91.076 ns	16,382.64 ns	0.0916	-	-	201 B
Solution.WithDocumentText	100	14,436.90 ns	355.846 ns	1,015.248 ns	14,392.68 ns	0.8240	0.2136	-	5285 B
Project.DocumentIds	10000	863,988.25 ns	1,297.511 ns	1,213.693 ns	863,625.88 ns	-	-	-	80 B
Project.Documents	10000	1,861,933.16 ns	11,538.506 ns	10,793.125 ns	1,859,064.65 ns	-	-	-	208 B
Solution.WithDocumentText	10000	14,088.55 ns	281.041 ns	453.828 ns	14,003.49 ns	0.8698	0.2289	-	5539 B

Measured on

BenchmarkDotNet=v0.12.1, OS=Windows 10.0.19042
AMD Ryzen Threadripper 3960X, 1 CPU, 48 logical and 24 physical cores
  [Host]     : .NET Framework 4.8 (4.8.4300.0), X64 RyuJIT
  DefaultJob : .NET Framework 4.8 (4.8.4300.0), X64 RyuJIT

[dibarbet]

mainly looks good, a few minor things

the WithDocumentText benchmarks looks like they increased more than the error, is that expected / problematic

[tmat]

the WithDocumentText benchmarks looks like they increased more than the error, is that expected / problematic

The difference is not significant. Modifying operations are much less important than read operations.

[tmat]

Oops, I have accidentally merged the commits of this PR in a follow-up PR: #51526

@dibarbet I'll send another PR that implements your suggestions.

[jasonmalinowski]

A semi-moot approval since this already merged by accident but ; thanks for doing this as this is a really, really nice cleanup that I'm sure was not fun doing the mechanical changes.

[tmat]

Superseded by #51526