[clangd] add inlay hints for std::forward-ed parameter packs

This adds special-case treatment for parameter packs in
make_unique-like functions to forward parameter names to inlay hints.
The parameter packs are being resolved recursively by traversing the
function body of forwarding functions looking for expressions matching
the (std::forwarded) parameters expanded from a pack.
The implementation checks whether parameters are being passed by
(rvalue) reference or value and adds reference inlay hints accordingly.
The traversal has a limited recursion stack depth, and recursive calls
like std::make_tuple are cut off to avoid hinting duplicate parameter
names.

Reviewed By: sammccall

Differential Revision: https://reviews.llvm.org/D124690