Support full keyboard layout customization

[toastal]

Is your feature request related to a problem? Please describe.
As a Dvorak user, wasd is actual at ,aoe. Small, but active alternative keyboard layout enthusiasts exist in pockets of the internet. Also there are accessibility concerns too that could be covered.

musehq/spacesvr#32

This merge request works for getting the keyboard layout but it requires Navigator.keyboard and getLayoutMap which isn't supported by Gecko-based browsers currently and would likely be reporting 'wrong' with resistFingerPrinting: true privacy setting even if support had landed.

Describe the solution you'd like
Like a video game, I want the ability to modify all actionable keys while maintaining my preferred key layout so I can use chat. Ideally, the defaults for QWERTY would still show in the UI as I prefer to just map them 1-to-1.

Describe alternatives you've considered
Swapping keyboard layouts via shortcut at the OS level depending on the task at hand. This is slow and leads to errors if I forget to swap.

[toastal]

Eh, probably covered by #2651 I used the wrong search query. Though I would prefer full, not lightweight, keyboard management.