[M148] [Pipewire] Fix mouse cursor data race.

Original change's description:
> [Pipewire] Fix mouse cursor data race.
>
> This addresses a potential data race when the mouse cursor is updated
> on the Pipewire thread and read by the capture thread.
>
> Bug: chromium:504551032
> Change-Id: I1afb9febe8bb41ce62c63872e2cb5514e908dd38
> Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/465440
> Reviewed-by: Tomas Gunnarsson <tommi@webrtc.org>
> Commit-Queue: Tomas Gunnarsson <tommi@webrtc.org>
> Auto-Submit: Mark Foltz <mfoltz@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#47502}

(cherry picked from commit 90b22181ec922900e26de71463b8e0ed47a5c2dd)

Bug: chromium:505447260,chromium:504551032
Change-Id: I1afb9febe8bb41ce62c63872e2cb5514e908dd38
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/468140
Commit-Queue: rubber-stamper@appspot.gserviceaccount.com <rubber-stamper@appspot.gserviceaccount.com>
Auto-Submit: Chrome Cherry Picker <chrome-cherry-picker@chops-service-accounts.iam.gserviceaccount.com>
Bot-Commit: rubber-stamper@appspot.gserviceaccount.com <rubber-stamper@appspot.gserviceaccount.com>
Cr-Commit-Position: refs/branch-heads/7778@{#6}
Cr-Branched-From: ca896b7ffef011bbf6957c99d413c5aac602c99f-refs/heads/main@{#47319}