feat(hid) Basic support for generic desktop usage page

[angweekiat]

Add basic support for "Generic Desktop" page, behind a ZMK_HID_GENERIC_DESKTOP_USAGES_BASIC KConfig, that works over USB and BLE, in particular for only 15 keys:

SYSTEM_POWER_DOWN	SYSTEM_SLEEP	SYSTEM_WAKE_UP	SYSTEM_CONTEXT_MENU	SYSTEM_MAIN_MENU
SYSTEM_APP_MENU	SYSTEM_MENU_HELP	SYSTEM_MENU_EXIT	SYSTEM_MENU_SELECT	SYSTEM_MENU_RIGHT
SYSTEM_MENU_LEFT	SYSTEM_MENU_UP	SYSTEM_MENU_DOWN	SYSTEM_COLD_RESTART	SYSTEM_WARM_RESTART

See Section 4 of https://www.usb.org/sites/default/files/hut1_5.pdf for the full list of possible usages. Verified that system keys are intercepted by the host machine using evtest, even though the machine doesn't do anything in response to most buttons, outside of SYSTEM_POWER_DOWN and SYSTEM_SLEEP.

Note

Upon coming across #1535 where the mute button was mentioned, I initially extended the work to additionally include up to 32 keys in total:

• System Dock (0xA0) to System Microphone Mute (0xA9),
• System Display Invert (0xB0) to System Display Swap Primary/Secondary (0xB6).

However, the linux machine that I'm testing on doesn't support the additional keys (uname -r -> 5.15.0-72-generic). If there's interest in these keys, and testing that it works, I'm happy to update the PR to include them. (I won't be able to test the keys myself)

Note 2

There's quite a bit of similar looking code between how the different keyboard, consumer, hid indicator, generic desktop pages are handled, across the relevant files. It may be possible to clean up some of the duplication if that's wanted, probably in a follow up PR.

Also, given that SYS_PWR and the other 2 system keys are already defined, maybe it's better if the config is set to true by default, or removed?

Test steps

• Flash central device with ZMK_HID_GENERIC_DESKTOP_USAGES_BASICenabled, with key map that uses the system keys above
• Re-pair the keyboard's Bluetooth connection, due to new attributes being added
• Try out the system keys! (Use evtest to verify that system events are coming in)