Reland "[ios] noncq to run tests on 14.0 simulators"

This is a reland of 297abb5adf2f4649c01fa34a0bb325fd806de751.

Added the xctest argument for iOS unit tests such that they
are triggered using the correct test runner.

Original change's description:
> [ios] noncq to run tests on 14.0 simulators
>
> ios-simulator-noncq to compile with xc12b5 as well.
> Running iOS 14.0 simulators for our test suites on xc12b5.
>
> Change-Id: I7ca5f763174c296278401ae3563894a4f5210379
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2367792
> Commit-Queue: Jeff Yoon <jeffyoon@chromium.org>
> Reviewed-by: Garrett Beaty <gbeaty@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#800739}

Change-Id: Ieb214a3e7788a551258470c1fb076e6603343384
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2370165
Commit-Queue: Jeff Yoon <jeffyoon@chromium.org>
Commit-Queue: Justin Cohen <justincohen@chromium.org>
Reviewed-by: Garrett Beaty <gbeaty@chromium.org>
Cr-Commit-Position: refs/heads/master@{#801130}