Use only one RaceChecker as intended with the original change. This gets
rid of specific RaceChecker for PipeWire members. Make PipeWireSession
guarded by API checker instead, since this member is accessed only in
[Start/Stop]Capture and move the race checker within PipeWire thread
loop lock. Also remove race check from OnStreamStateChanged where we
only modify one property guarded by API mutex.
Partially reverts a9d497b52dc21497fdfd0e8c03ab2f8559e02d15 reviewed
on https://webrtc-review.googlesource.com/c/src/+/326781.
Bug: webrtc:15181
Change-Id: I46449fce86611124688a65d5337771c75853f2ca
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/338021
Reviewed-by: Ilya Nikolaevskiy <ilnik@webrtc.org>
Commit-Queue: Jan Grulich <grulja@gmail.com>
Cr-Commit-Position: refs/heads/main@{#41713}
541f202354