Currently UI code always has to use char pointers when interacting with
the translation system. This makes benefiting from the use C++ strings
and StringRef more difficult. That means we're leaving some type safety
and performance on the table. This PR adds StringRef overloads to the
translation API functions and removes the few calls to `.c_str()` that
are now unnecessary.
Pull Request: https://projects.blender.org/blender/blender/pulls/133887