[global-shortcut] Ability to bind mouse back/forward (m4/m5) buttons

### Describe the problem

Usecase: push-to-talk or toggle mute in a voice chat app. Having it bound to a side back/forward mouse button is extremely convenient, especially in-game. Discord supports that

### Describe the solution you'd like

It would work pretty much the same as the regular mappings, e.g. completely capturing the key on windows, not passing it to other apps. I'm also personally fine if this feature is not cross-platform, but I don't know the projects stance on this

### Alternatives considered

This could be worked around using external software, e.g. mapping the mouse buttons to inaccessible F13+ keys, but that is an extremely bad user experience

### Additional context

Wasn't able to find an issue on this, tho it doesn't seem like something too uncommon. I might be willing to work on this in the future, but windows and linux only and I don't have too much experience with how input is handled on either of those systems