Now that we're parsing Foundation in every swift2objc run, the runs have gotten a lot slower. On my laptop, parsing Foundation takes 5-10sec, but on github CI it takes minutes.

Instead of parsing this symbolgraph each time, we could store the pre-parsed AST. I think the biggest chunk of time is just the swiftc command to extract the symbolgraph JSON from the precompiled module. So we could just check that JSON in as part of the package repo.

For even more time savings, we could add something like python's repr to swift2objc's AST nodes, to codegen const objects for the whole Foundation AST.