SAL annotations are incorrectly being interpreted as Optional

[kennykerr]

The SAL annotation for IWeakReferenceSource.GetWeakReference indicates that its parameter is __RPC__deref_out_opt, which indicates that the caller must provide a valid pointer - it is not optional - but that it may return a null pointer back to the caller. The two canonical implementations (WRL and C++/WinRT) both treat it as required and will AV if a valid pointer is not provided.

The metadata should remove the [Optional] attribute to correctly describe APIs with this annotation.

[kennykerr]

This seems to be a much larger problem of misapplying [Optional] to certain SAL annotations. For example, IMLOperatorKernelContext.GetInputTensor is said to have an optional out parameter but that's not what the _COM_Outptr_result_maybenull_ annotation means. That annotation means that the parameter is required but that null may be returned to the caller.

[riverar]

Think #803 is also related, and overall related to SAL annotation parser needing some tweaks.

win32metadata/sources/ClangSharpSourceToWinmd/MetadataSyntaxTreeCleaner.cs

Lines 779 to 807 in e20e414

	else if (salAttr.P1.StartsWith("__RPC__"))
	{
	// TODO: Handle ecount, xcount and others that deal with counts
	string[] parts = salAttr.P1.Split('_');
	foreach (var part in parts)
	{
	switch (part)
	{
	case "in":
	isIn = true;
	break;
	case "out":
	isOut = true;
	break;
	case "inout":
	isIn = isOut = true;
	break;
	case "opt":
	isOpt = true;
	break;
	}
	}
	break;
	}