Changes

[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