Handle the warnings in R2RDump

[cshung]

In order to extract the parsing code from R2RDump to a separate library, I silenced a couple of warnings from the code in #267. This issue is filed to track the work to surface the warning in some TBD way.

runtime/src/coreclr/src/tools/crossgen2/ILCompiler.Reflection.ReadyToRun/R2RHeader.cs

Lines 89 to 93 in 1e38424

	if (!Enum.IsDefined(typeof(R2RSection.SectionType), type))
	{
	// TODO (refactoring) - what should we do?
	// R2RDump.WriteWarning("Invalid ReadyToRun section type");
	}

runtime/src/coreclr/src/tools/crossgen2/ILCompiler.Reflection.ReadyToRun/Amd64/UnwindInfo.cs

Lines 240 to 244 in 1e38424

	if ((UnwindCodeArray[i].FrameOffset & 0xF0000000) != 0)
	{
	// TODO (refactoring) - what should we do?
	// R2RDump.WriteWarning("Illegal unwindInfo unscaled offset: too large");
	}

In general, the R2RDump tool is not robust against malformed files, we do not expect any of those appears in the wild. Here is a similar issue for handling missing reference assembly.

https://github.com/dotnet/coreclr/issues/27564