[clang-tools-extra] Extend support for specifying languages and version in add_new_check.py (PR #100129)

[Nathan James via cfe-commits]

njames93 wrote:

Having a default in there is important to help people understand how to use it. But, you're right, maybe we should document this so that people won't fall into this trap.

https://github.com/llvm/llvm-project/pull/100129