[Breakpoint] Make breakpoint language agnostic

Summary:
Breakpoint shouldn't need to depend on any specific details from a
programming language. Currently the only language-specific detail it takes
advantage of are the different qualified names an objective-c method name might
have when adding a name lookup. This is reasonably generalizable.

The current method name I introduced is "GetVariantMethodNames", which I'm not
particularly tied to. If you have a better suggestion, please do let me know.

Reviewers: JDevlieghere, jingham, clayborg

Subscribers: mgorny, lldb-commits

Differential Revision: https://reviews.llvm.org/D61746

llvm-svn: 360509