Use BenchmarkDotNet instead of the custom PerfTester

[WojciechNagorski]

In this PR I used BenchmarkDotNet instead of custom PerfTest. Thanks to it we have:

• MemoryDiagnoser
• More reliable data - more info Pro .NET Benchmarking

Results BenchmarkDotNet=v0.12.1, OS=Windows 10.0.18362.1082 (1903/May2019Update/19H1) Intel Core i7-8565U CPU 1.80GHz (Whiskey Lake), 1 CPU, 8 logical and 4 physical cores .NET Core SDK=5.0.100-rc.1.20452.10 [Host] : .NET Core 3.1.2 (CoreCLR 4.700.20.6602, CoreFX 4.700.20.6702), X64 RyuJIT DefaultJob : .NET Core 3.1.2 (CoreCLR 4.700.20.6602, CoreFX 4.700.20.6702), X64 RyuJIT

Method	Mean	Error	StdDev	Gen 0	Gen 1	Gen 2	Allocated
BuildDiffModel	32.23 ms	0.569 ms	0.505 ms	1031.2500	437.5000	156.2500	6.24 MB

Limitations I didn't want to change the behavior of the benchmark so it still generates different examples during runtime. It is not a good pattern.

How to run

cd Perf.DiffPlex
dotnet run -c Release -- --filter *