Benchmark parameter disposal

[mawosoft]

See https://github.com/mawosoft/BenchmarkDotNet.Tests/tree/master/BDNParamDisposal
for parameter/argument creation and disposal in BDN host and in generated projects.

The generated code does not dispose the actually used parameters/arguments at all. Disposal occurs only while enumerating a ParamsSource or ArgumentsSource to skip to the current one and only for the ones skipped:

BenchmarkDotNet/src/BenchmarkDotNet/Parameters/SmartParamBuilder.cs

Lines 145 to 162 in a5176a7

	foreach (T parameter in parameters)
	{
	if (count == index)
	{
	return parameter;
	}
	if (parameter is IDisposable disposable)
	{
	// parameters might contain locking finalizers which might cause the benchmarking process to hung at the end
	// to avoid that, we dispose the parameters that were created, but won't be used
	// (for every test case we have to enumerate the underlying source enumerator and stop when we reach index of given test case)
	// See https://github.com/dotnet/BenchmarkDotNet/issues/1383 and https://github.com/dotnet/runtime/issues/314 for more
	disposable.Dispose();
	}
	count++;
	}

BDN host only disposes benchmarks it actually runs and only after they all have been run:

BenchmarkDotNet/src/BenchmarkDotNet/Running/BenchmarkRunnerClean.cs

Lines 111 to 117 in 38b99b9

	// some benchmarks might be using parameters that have locking finalizers
	// so we need to dispose them after we are done running the benchmarks
	// see https://github.com/dotnet/BenchmarkDotNet/issues/1383 and https://github.com/dotnet/runtime/issues/314 for more
	foreach (var benchmarkInfo in benchmarkRunInfos)
	{
	benchmarkInfo.Dispose();
	}

The IDisposable chain goes: BenchmarkRunInfo -> BenchmarkCase(s) -> ParameterInstances -> ParameterInstance(s) -> (Value as IDisposable)?

However, BenchmarkCase(s) - and therefore ParameterInstance(s) - have been already created early and have gone through filters and validators.

• If some are filtered out, they are not disposed.
• If any validator reports a critical error, none are disposed at all.

The problem is that ParameterInstance(s) are constructed per method. Multiple job definitions share the same cached instances. Thus a filtered BenchmarkCase cannot be disposed because it might share ParameterInstance(s) with benchmarks that are about to be run.