.clang-tidy: Add basic .clang-tidy for identifier naming

[antangelo]

Adds a .clang-tidy config that covers most identifier naming conventions. Ideally we can offload this component of PR reviews to CI along with formatting in #1510 .

Unfortunately it doesn't seem like clang-tidy supports having a separate option for global static variables vs global non-static variables (from what I can tell the StaticVariable option only applies to locals), so one limitation of this config is that it will recommend the g_ prefix for global static variables. The alternative is not to enforce a naming convention on the clang-tidy level, but we'd have to continue doing so manually in PR reviews.