[Validation] Introduce validation diagnostics in DxilMetadataHelper.cpp

Is your feature request related to a problem? Please describe.
DxilMetadataHelper.cpp is used in assembling the DXIL Container, which is a step that happens before DXIL Validation. There are several validation rules that should be tested in DXILValidation.cpp, but these validation rules are assumed to hold in parsing and constructing the DXILContainer in DxilMetadataHelper.cpp. DxilMetadataHelper.cpp has no validation diagnostics, it simply assumes these validation rules are true, and if they aren't, the validator fatally crashes without any helpful diagnostics.

Describe the solution you'd like
We need to introduce a way to emit validation diagnostics in DxilMetadataHelper.cpp, because we need to test our validation rules.

Describe alternatives you've considered
Another alternative is to redesign all of validation so that some DXIL validation happens before container assembly, then container assembly happens, then the rest of the DXIL Validation (if any depends on the container being assembled) gets tested.

Additional context
This issue was inspired in https://github.com/microsoft/DirectXShaderCompiler/issues/6161 because of the inability to test if the wavesize range tag in the DXIL has 3 arguments. In DxilMetadataHelper.cpp, in LoadDxilEntryProperties, when the wavesize range tag is read, it is assumed that there are 3 integer arguments. We cannot assume this, and need validation errors to be emitted if this is not the case. However, we cannot emit these diagnostics because there are no methods by which to emit them in the entire cpp file.

Start in DxilMetadataHelper.cpp, especially LoadDxilEntryProperties and its handling of the wavesize range tag, then compare the related validation rules in DXILValidation.cpp. Define how malformed metadata should emit validation diagnostics instead of causing a fatal crash, with the three-argument wavesize case from issue 6161 as the concrete completion check.