Reland "Reparent glic widget to nullptr when detached (Mac)."

This is a reland of commit 7e8ffca9fc6cd3fb3a9d77276362127b1d42d8da

Changed the BUILDFLAG inside the test to only compile on Mac.

The dragging issue that the original CL addresses (crbug.com/394149236) is mac-only. On win11, these tests time out when calling WaitForDisplaySizes() during virtual display set up, but that is not needed on Windows.

Original change's description:
> Reparent glic widget to nullptr when detached (Mac).
>
> This makes the detached glic widget to a top-level widget and allows for dragging across multiple displays.

Change-Id: Ieeb71cc9392ff9e0057afc679efd1cac2b7e558f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6253646
Commit-Queue: Sana Akbani <sanaakbani@google.com>
Reviewed-by: Keren Zhu <kerenzhu@chromium.org>
Reviewed-by: Erik Chen <erikchen@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1419485}