Re-enable middle click scrolling mac disabled web tests.

There are 17 middle-click auto-scroll web tests, with five currently
disabled on Mac. I ran these tests locally, and they all passed. To
ensure reliability, I executed them 500 times (using --iterations=50
and --repeat-each=10), and they consistently passed. Therefore, it
appears safe to re-enable these tests.

Bug: 40589357
Change-Id: I6cf95f439031e3260e23a7cedabe2872fb5f499b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5824711
Reviewed-by: Kevin Ellis <kevers@chromium.org>
Commit-Queue: Gaston Rodriguez <gastonr@microsoft.com>
Cr-Commit-Position: refs/heads/main@{#1348717}