ANDROID: Sync proxy-exec logic to v19 (from v18)

Just aligning android16-6.12 tree to the changes
made in proxy-exec v19.

v18 series:
https://github.com/johnstultz-work/linux-dev/commits/proxy-exec-v18-6.12

v19 series:
https://github.com/johnstultz-work/linux-dev/commits/proxy-exec-v19-6.12



Changes since v18:
* Build fixup for PREEMPT_RT suggested by K Prateek Nayak
* Slight re-arrangement of functions to clean up later patches
* Slight tweak further simplifying update_curr_common() suggested by Peter
* Rename try_to_block_task() arguments and add additional comments
  suggested by Peter
* Push proxy_resched_idle() returning rq->idle to a later patch in the
  series, as suggested by Peter.
* Build fixup for !CONFIG_SMP and CONFIG_SCHED_PROXY_EXEC
* Fixed proxy_force_return() logic for !SMP cases

Bug: 431329485
Change-Id: I3dd8ddab236f9c1b68e2495a4023f5b474265aa6
Signed-off-by: John Stultz <jstultz@google.com>