Support high precision in TaskQueueGcd delayed tasks

TaskQueueGcd previously ignored PostDelayedTaskTraits::high_precision
and scheduled all delayed tasks with dispatch_after_f(), which is
subject to OS timer coalescing (up to 100 ms under background policy).

Schedule high-precision delayed tasks using a one-shot
DISPATCH_TIMER_STRICT timer source with leeway capped at 1 ms. Low-
precision tasks continue to use dispatch_after_f().

Bug: webrtc:470337728
Change-Id: Iafd6b1296d6bcd2446c3fade1f624907128e684a
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/510942
Commit-Queue: Tomas Gunnarsson <tommi@webrtc.org>
Reviewed-by: Markus Handell <handellm@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#49042}