[clangd] Wait for compile command in ASTWorker instead of ClangdServer

Summary:
This makes addDocument non-blocking and would also allow code completion
(in fallback mode) to run when worker waits for the compile command.

Reviewers: sammccall, ilya-biryukov

Reviewed By: ilya-biryukov

Subscribers: javed.absar, MaskRay, jkorous, arphaman, kadircet, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D60607

git-svn-id: https://llvm.org/svn/llvm-project/clang-tools-extra/trunk@358400 91177308-0d34-0410-b5e6-96231b3b80d8
9 files changed