[clangd] Replay preamble #includes to clang-tidy checks.

Summary:
This is needed to correctly handle checks that use IncludeInserter,
which is very common.

I couldn't find a totally safe example of a check to enable for testing,
I picked modernize-deprecated-headers which some will probably hate.
We should get configuration working...

This depends on D54691 which ensures our calls to getFile(open=false)
don't break subsequent accesses via the FileManager.

Reviewers: ilya-biryukov

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

Differential Revision: https://reviews.llvm.org/D54694

llvm-svn: 347298