chore: Fix benchmark TestAdapter related issues

[filzrev]

This PR intended to fix BenchmarkDotNet.TestAdapter related issues.

What's changed in this PR

1. Modify System.Collections.Immutable baseline version from 9.0.3 -> 9.0.0 and modify related benchmark.
2. Add AppDomain.CurrentDomain.AssemblyResolver for .NET 4.6.2 on TestAdapter project to fix assembly loading issue.
3. Remove explicit PackageReference to System.Memory (Use transitively referenced package version instead)

Background
System.Collections.Immutable is transitively referenced by other packages.
And it cause version conflicts when using TestAdapter. So it need to adjust minimum version to other packages.
(Normally it's not cause issue Because newer version is loaded first. But when running with TestAdapter. It seems 9.0.0 version is loaded and cause conflicts)

And when using TestAdapter on .NET 4.6.2.
It failed to load BenchmarkDotNet.dll.
So I've added custom AssemblyResolve for net462.

I've confirmed this issue on following condigitons.

1. Run BenchmarkDotNet.Samples project with following command.
    > dotnet test -c Release --list-tests --framework net462 -tl:off
2. When using `BenchmarkDotNet.TestAdapter` package and targeting .NET Framework.

[timcassell]

We may want to refactor the test adapter to use the new Microsoft.Testing.Platform instead of the old VSTest at some point.

[filzrev]

We may want to refactor the test adapter to use the new Microsoft.Testing.Platform instead of the old VSTest at some point.

To migrate from VSTest to Microsoft.Testing.Platform.
It need to migrate to use xunit.v3 packages.

And xunit.v3 2.x or later supports following runtimes as minimum requirements.

.NET Framework 4.7.2 (or later)
.NET 8 (or later)
Our target frameworks for v3 currently are:

.NET Standard 2.0 (netstandard2.0)
.NET Framework 4.7.2 (net472)
.NET 8 (net8.0)
Also new for v3: Mono is officially supported on Linux and macOS for .NET Framework test projects. While it did often work with v1 and v2, we do officially test and verify with it now.

So it need to drop legacy runtimes supports when migrating to Microsoft.Testing.Platform.
Personally, I think it is reasonable to periodically drop out-of-support runtimes supports for future maintenance cost.

[timcassell]

I don't understand. TestAdapter doesn't use xunit, and Microsoft.Testing.Platform supports netstandard2.0.

[filzrev]

Thanks for your confirmations.
I misunderstood that TestAdapter depends on the xUnit discovery feature.