[swift2objc] More little fixes

[liamappelbe]

• The ModuleInputConfig symbolgraph command should use swift, not swiftc
• Dedupe class methods by ID, to fix multiple definition issues
• Also dedupe methods by their full name (name + arg names), to work around this buggy API conflicting with this other API
• Hard code a list of methods that we don't try to wrap, such as hashValue, because these are special cased in Swift, and we're not allowed to override them

I don't really have a way of testing these changes, since they're mostly dealing with bugs in the apple APIs that I'm not sure how to replicate in Swift source without compile errors. Once I get the end-to-end demo working I'll add an integration test that wraps a real Apple API.

[coveralls]

coverage: 92.065% (-0.1%) from 92.189% when pulling 338f9453c55f276982dd5686db63ef7834abc65b on moreswift2objcfixes into 069c91033a104cc13a6a57eda372ed8c82f21b40 on main.