[clang-tidy] Improve bugprone-unused-return-value check

Summary:
Add support for checking class template member functions.

Also add the following functions to be checked by default:

- std::unique_ptr::release
- std::basic_string::empty
- std::vector::empty

Reviewers: alexfh, hokein, aaron.ballman, ilya-biryukov

Reviewed By: aaron.ballman

Subscribers: jbcoe, xazax.hun, cfe-commits

Tags: #clang-tools-extra

Differential Revision: https://reviews.llvm.org/D45891

Patch by khuttun (Kalle Huttunen)

llvm-svn: 330772