A couple of follow ups to #12833:

1. Try to make the API a bit cleaner with templating: tls: simplify implementation and fix one class of crashing bug #12833 (comment)
2. Build clang-tidy plugin to check for any TLS functions capturing "this", and fix all current examples. (There are several that capture "this" in the initial set() call, and some that have been "fixed" to use shared_from_this and weak_ptr.)