Use IDL to generate COM API

[namandixit]

COM was originally designed to make language bindings easier. But the current way of doing COM in this project is the worst of both worlds: it adds all the superficial complexity of COM without providing any of the actual features of COM.

Since Slang API follows COM, it might make more sense to have that API be generated through IDL files. That way, the COM API can be used from C directly (see here for instructions on how). IDL generated headers also come with a COBJMACROS define guard that includes some helper macros to make COM headers easy to use with C.

This will allow C and any programming language with a C-compatible FFI to simply use the library directly, instead of either using the deprecated C API or write wrappers around C++ API (both of which may break with updates).

Relevant: #6184

[expipiplus1]

This is a definitely a desirable change to make, I've opened this issue to track it, however it's not currently on the near term roadmap #8356