Feature request: Support generic desktop usage page

[urob]

Currently, only the "keyboard/keypad" and "consumer" pages are supported (https://github.com/zmkfirmware/zmk/blob/main/app/src/hid.c#L237-L245).

Supporting the "generic desktop" usage page would allow using various system-related keys, some of which are already defined but not operational (https://github.com/zmkfirmware/zmk/blob/main/app/include/dt-bindings/zmk/keys.h#L12-L22).

Related: #1077

[chrissicool]

I was looking for a key code to mute the microphone. Then I found this issue, because the USB HID specification was updated recent'ish [1] to add a system microphone mute code. But it's a system-related key and is part of the "Generic Desktop" usage page. Looks like there is one more interesting key to unlock with that feature.

At least Linux is able to handle this starting from v6.3. I don't know about other OSes.

[1] https://www.usb.org/sites/default/files/hutrr110-systemmicrophonemute.pdf

[angweekiat]

Hi, I tried my hand at this, and the changes are viewable in the PR above, please give it a try / test it out!