[Proposal] Expose the Debug Interface Access API

[Benjamin Moir]

Description

https://docs.microsoft.com/en-us/visualstudio/debugger/debug-interface-access/debug-interface-access-sdk
This is a set of COM APIs covering the parsing of PDB files. The headers are typically located in %VSInstallDir%\DIA SDK\include (when the C/C++ tools are installed). It may also be worthwhile to expose the DbgHelp APIs, which are higher level wrappers over DIA.

Rationale

I make use of DIA in several projects I'm working on with C# where performance is a significant factor, thus it would be immensely helpful for the APIs to be available in low-level blittable form via TerraFX.

Drawbacks

The msdia*.dll (and dbghelp.dll) libraries are not typically available from PATH, and are usually only present when Visual Studio has been installed with the C/C++ tools workload. This could complicate general usage (though I suppose it could be mitigated with a NuGet package providing the DLLs?), since you would likely need to register a custom resolver for the APIs to work.

Alternatives

Currently you can generate a (non-blittable) binding for DIA by using midl and tlbimp, but several of the APIs end up being unwieldy (or potentially unusable) due to the resulting signatures using managed arrays, refs, etc.