[Shortcuts]: On macOS you can't create shortcuts with the Command key

[fallaciousreasoning]

This is because the key is sent to the backend as Meta but the backend only knows how to parse Command

[stephendonner]

Verification PASSED using

Brave	1.53.81 Chromium: 114.0.5735.90 (Official Build) beta (x86_64)
Revision	386bc09e8f4f2e025eddae123f36f6263096ae49-refs/branch-heads/5735@{#1052}
OS	macOS Version 11.7.7 (Build 20G1345)

Steps:

1. installed 1.53.81
2. launched Brave
3. opened brave://flags
4. set brave://flags/#brave-commands to Enabled
5. clicked Relaunch
6. loaded brave://settings/system
7. clicked on Shortcuts (brave://settings/system/shortcuts)
8. deleted the binding for Focus Location
9. deleted the binding for New Tab
10. clicked on Add next to New Tab
11. pressed command + L
12. clicked Save
13. confirmed New Tab shows Command L
14. pressed Command + L
15. confirmed it opened a new-tab window
16. while I was here, confirmed I could reset both New Tab and Focus Location bindings

example	example	example	example	example	example	example

[fallaciousreasoning]

Note: JavaScript sometimes requires other keys to be pressed to register Meta key presses. For example, if I just press the Meta key on Linux, the shortcuts UI doesn't get any input which is a bit weird to me. I get the same results in https://css-tricks.com/snippets/javascript/javascript-keycodes/

If this turns out to be a big problem, we can add a special mojom interface, just for this and not use the existing JS key handlers.