[clangd] Unify printing policy for type hints

(This patch addresses the comment from https://reviews.llvm.org/D151785#4402460.)

Previously, we used a special printing policy that enabled `PrintCanonicalTypes`
to print type hints for structure bindings. This was intended to
eliminate type aliases like `tuple_element::type`. However, this also
caused TypePrinter to print default template arguments, which could
result in losing the ability to see types like `std::basic_string<char>`
if the fully expanded template-id exceeded the default inlay hint threshold.

Simply getting the canonical type at the call site could help us get rid of
the side effect.

This also merges overloaded `addTypeHint` into one function without
`PrintingPolicy`.

Reviewed By: nridge

Differential Revision: https://reviews.llvm.org/D152520