[clangd] Get rid of regexes in CanonicalIncludes

Summary: Replace them with suffix mappings.

Reviewers: ioeric, kbobyrev

Reviewed By: ioeric

Subscribers: MaskRay, jkorous, arphaman, jfb, kadircet, cfe-commits

Differential Revision: https://reviews.llvm.org/D51088

llvm-svn: 340410