[clangd] Pass file when possible to resolve URI.

Some URI scheme needs the hint path to do a correct resolution, we pass
one of the open files as hint path.

This is not perfect, and it might not work for opening files across
project, but it would fix a bug with our internal scheme.

in the long run, removing URIs from all the index internals is a more proper fix.

Differential Revision: https://reviews.llvm.org/D96844