[clang-rename] Fix the missing template constructors.

Summary:
When renaming a class with template constructors, we are missing the
occurrences of the template constructors, because getUSRsForDeclaration doesn't
give USRs of the templated constructors (they are not in the normal `ctors()`
method).

Reviewers: kbobyrev

Subscribers: jkorous, arphaman, kadircet, usaxena95, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D74216