Disallow shared workers on Android

Removes shared worker WebGPU tests from Android testers and adds a
runtime check to make it obvious what shared workers are not supported
on Android.

Bug: dawn:2486, 330501141
Change-Id: I2a212cf7f2e61856a223d304ceebac618dc4ceb4
Validate-Test-Flakiness: skip
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5422508


Commit-Queue: Kai Ninomiya <kainino@chromium.org>
Reviewed-by: Kai Ninomiya <kainino@chromium.org>
Auto-Submit: Brian Sheedy <bsheedy@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1282773}