[clangd] Get rid of Inclusion::R

Summary:
This is only used by documentlink and go-to-definition. We are pushing
range detection logic from Inclusion creation to users. This would make using
stale preambles easier.

For document links we make use of the spelledtokens stored in tokenbuffers to
figure out file name range.

For go-to-def, we keep storing the line number we've seen the include directive.

Reviewers: sammccall

Subscribers: ilya-biryukov, MaskRay, jkorous, arphaman, usaxena95, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D79315