mac: enable ImmersiveFullscreen by default

Bug: 40059835
Change-Id: Iac1ade4bdf064ed071b81110d4025418383c460b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5622512


Commit-Queue: Leonard Grey <lgrey@chromium.org>
Commit-Queue: Tom Burgin <bur@google.com>
Auto-Submit: Tom Burgin <bur@google.com>
Reviewed-by: Leonard Grey <lgrey@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1313599}