[clangd] Implement rename by using SelectionTree and findExplicitReferences.

Summary:
With the new implemenation, we will have better coverage of various AST
nodes, and fix some known/potential bugs.

Also added the existing clang-renamae tests. Known changed behavior:
 - "~Fo^o()" will not trigger the rename, will fix afterwards
 - references in macro bodies are not renamed now

This fixes:
- https://github.com/clangd/clangd/issues/167
- https://github.com/clangd/clangd/issues/169
- https://github.com/clangd/clangd/issues/171

Reviewers: ilya-biryukov

Subscribers: MaskRay, jkorous, arphaman, kadircet, usaxena95, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D69934