Move global shortcut listener to //ui/base

Preparing this for use by features other than extensions. Due to how
extensions-specific the Linux handling is, I made a base class with
the windows, mac, and ozone implementations which is then used by the
extensions listener.

In a followup CL I'll move the linux implementation after I can update
it to be generalized (by moving extensions::Command). This will be
used by another feature in //chrome/browser but I chose to put it in
//ui/base because other closely related accelerator logic lives there.

Follow-up work includes:
1. Migrate extensions::Command to ui::Command
2. Migrate global_shortcut_listener_linux to //ui/base
3. Rename extensions::GlobalShortcutListener


Bug: 378487333
Change-Id: I998f50a51420ff22170fa56fcaa2a10ae09ad8da
Low-Coverage-Reason: TRIVIAL_CHANGE the low coverage file is just being moved
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6050596
Reviewed-by: Peter Boström <pbos@chromium.org>
Reviewed-by: Eshwar Stalin <estalin@chromium.org>
Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Commit-Queue: Alison Gale <agale@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1396808}