[scudo] Add new fast purge option. (#175266)

This adds a new option to do a faster of a purge.

When doing a release to OS due to a purge call, if another thread is
also doing a release, the call can be blocked while that operation
concludes. In some cases, code wants a fast version that releases as
fast as possible and the call will not block.

For example, on Android, when destroying a Bitmap a purge occurs to save
memory. But this can cause some jank if the purge takes too long.

In the future, I envision that this option will also do a calculation to
stop purging after some cutoff value to avoid being blocked in this call
for too long.

GitOrigin-RevId: a816f922fa73828b24008a8cdd0a28448eed68ef