For example, lots of files only use AUTO_PROFILER_LABEL, so they don't need all the extra baggage that comes with GeckoProfiler.h (and/or BaseProfiler.h).

Markers already have their own header, but it still relies on some BaseProfiler.h definitions, and some forward declarations (e.g., profiler_current_thread_id()), which could be moved to a header with these generic functions.

Some benefits:

• Smaller headers, easier for developers to grasp.
• Functions related to the same domain would be together without noise from other domains.
• Users can include only particular headers for their needs, which should slightly reduce compilation time.