[clangd] Refactor ProtocolHandlers to decouple them from ClangdLSPServer
Summary:
A refactoring to decouple ProtocolHandlers and Language Server input parsing
loop from the ClangdLSPServer.
The input parsing was extracted from `main` to a function(runLanguageServerLoop).
ProtocolHandlers now provide an interface to handle various LSP methods,
this interface is used by ClangdLSPServer.
Methods for code formatting were moved from ProtocolHandlers to ClangdServer.
ClangdLSPServer now provides a cleaner interface that only runs Language Server
input loop.
Reviewers: bkramer, krasimir
Reviewed By: krasimir
Subscribers: cfe-commits, klimek
Tags: #clang-tools-extra
Differential Revision: https://reviews.llvm.org/D33201
llvm-svn: 303173