Expedite jobs for PRE_UNSUBSCRIBE actions.

Use `setImportantWhileForeground` between SDK versions 28, 29, and 30;
use `setExpedited` from SDK version 31 and above, and do nothing for
versions <= 27, as the one-tap unsubscribe feature is not supported.

Changes were manually end-to-end tested on Android 28, 31, and 34.

Bug: 324827395
Change-Id: I3d9e5fd0c05260111fc0cd390f0ca66a46bf13b8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5432933


Auto-Submit: Balazs Engedy <engedy@chromium.org>
Commit-Queue: Peter Beverloo <peter@chromium.org>
Reviewed-by: Peter Beverloo <peter@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1283627}