Let the module-rt and module-rtkit provide a new pw_thread_utils
implementation.
The pw_thread_utils interface has many advantages over the old way
of boosting the thread:
1. Does not require to add a source to the loop and do priority
boost in-thread.
2. Works on simple threads without data-loop interface.
3. Allows dropping RT priority as well.
The rtkit implementation requires a bit more work because there is
currently no pthread API to map an pthread to a tid. We make a small
wrapper thread to capture the tid with getpid() to do the mapping
ourselves. This should go when the new API arrives. See also:
(https://sourceware.org/bugzilla/show_bug.cgi?id=27880)
200ms seems a little small, some plugins initialize themselves from the
RT thread and get killed. 2 seconds seem to be a better default.
The important part is that there is a limit so that runaway processes
are killed and don't lock up the system.
Fixes#1344
