Making ir publicly accessible

Hi, I'd like to use bindgen to parse headers into ir without the codegen part, and then with ir I can generate bindings in other languages.

There is --emit-ir, but that's in debug format which is not easily readable by machines.

I think we can make the ir module public (may need some cleanup though), and/or add a --emit-ir-jsonoption to emit ir in json represetantion, something like:

{
   "kind": "function",
   "name": "foo",
   "mangledName": "_foo",
   "signature": {
      "returnType": ...,
      "params": [ ... ]
   },
}

I'd be happy to work on a PR, if such change doesn't fall out of bindgen's scope.

Start by inspecting the existing --emit-ir entry point and the ir module to understand how the current debug representation is produced. Compare the two proposed directions—making ir public or adding JSON emission—and define the supported machine-readable interface, including its scope and cleanup needs. Done means the chosen interface is usable for parsing bindgen IR without invoking code generation.