[clangd] Added highlighting for the targets in typedefs and using.
In typedef int A the A was not highlighted previously.
This patch gives A the same kind of highlighting that the underlying type has (class/enum) (which in this example is no special highlighting because builtins are not handled yet)
Will add highlightings for built ins in another patch.
Reviewers: hokein, sammccall, ilya-biryukov
Subscribers: MaskRay, jkorous, arphaman, kadircet, cfe-commits
Differential Revision: https://reviews.llvm.org/D64754