[clangd] Customizable URI schemes for dynamic index.

Summary:
This allows dynamic index to have consistent URI schemes with the
static index which can have customized URI schemes, which would make file
proximity scoring based on URIs easier.

Reviewers: sammccall

Reviewed By: sammccall

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

Differential Revision: https://reviews.llvm.org/D47931

git-svn-id: https://llvm.org/svn/llvm-project/clang-tools-extra/trunk@334809 91177308-0d34-0410-b5e6-96231b3b80d8
10 files changed