[clangd] Show template argument list in workspacesymbols and documentsymbols responses

Summary:
Last part of re-landing rC356541. Puts TemplateArgumentsList into
responses of the above mentioned two requests.

Reviewers: ioeric, ilya-biryukov

Subscribers: MaskRay, jkorous, arphaman, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D59641

llvm-svn: 358274