Add ProjectOperationBenchmarks

[sharwell]

Related to #48682

Baseline for net472:

BenchmarkDotNet=v0.12.1, OS=Windows 10.0.19042
Intel Core i7-9700 CPU 3.00GHz, 1 CPU, 8 logical and 8 physical cores
  [Host]     : .NET Framework 4.8 (4.8.4250.0), X64 RyuJIT
  DefaultJob : .NET Framework 4.8 (4.8.4250.0), X64 RyuJIT

Method	DocumentCount	Mean	Error	StdDev	Median	Gen 0	Gen 1	Gen 2	Allocated
Project.DocumentIds	0	30.56 ns	0.239 ns	0.224 ns	30.52 ns	-	-	-	-
Project.Documents	0	72.16 ns	0.546 ns	0.511 ns	72.12 ns	0.0204	-	-	128 B
Project.DocumentIds	100	5,808.83 ns	16.180 ns	15.135 ns	5,801.97 ns	0.0076	-	-	72 B
Project.Documents	100	23,940.13 ns	192.507 ns	170.652 ns	23,898.33 ns	0.0305	-	-	201 B
Project.DocumentIds	10000	630,369.55 ns	4,333.417 ns	3,841.461 ns	630,697.17 ns	-	-	-	80 B
Project.Documents	10000	4,625,697.37 ns	90,883.316 ns	181,503.802 ns	4,547,228.91 ns	-	-	-	256 B

Baseline for netcoreapp3.1:

Method	DocumentCount	Mean	Error	StdDev	Gen 0	Gen 1	Gen 2	Allocated
Project.DocumentIds	0	12.38 ns	0.060 ns	0.057 ns	-	-	-	-
Project.Documents	0	69.20 ns	0.326 ns	0.305 ns	0.0191	-	-	120 B
Project.DocumentIds	100	6,248.08 ns	39.344 ns	36.802 ns	0.0076	-	-	72 B
Project.Documents	100	20,200.63 ns	178.158 ns	166.649 ns	0.0305	-	-	192 B
Project.DocumentIds	10000	656,870.67 ns	4,355.570 ns	4,074.203 ns	-	-	-	72 B
Project.Documents	10000	3,936,493.63 ns	28,108.377 ns	26,292.594 ns	-	-	-	192 B