setvolume: detailed usage info, print mute state

* Describe parameters in "usage".
* Change -m to explicitely mute, instead of toggling mute.
* Add -t to toggle muting, -u to unmute.
* Add long version options:
--mute, --unmute, --togglemute --increase, --decrease
* Accept a step size as additional parameter to in/decrease,
without it, the step size is 3 dB.
* Print muting state when toggling or un/muting.
* Update shortcut_settings to use "setvolume -t" to toggle muting.

Change-Id: Iacad5bcf4a40a6056c85161ac45379015392420c
Reviewed-on: https://review.haiku-os.org/c/haiku/+/5976
Tested-by: Commit checker robot <no-reply+buildbot@haiku-os.org>
Reviewed-by: Adrien Destugues <pulkomandy@pulkomandy.tk>
Reviewed-by: nephele <nep@packageloss.eu>

Shortcuts: provide some default actions for mute, increment and decrement volume media keys

Works for HID-aware devices (USB & PS/2).

Change-Id: I45e9ededaab1699f30e55fb644ec0e3ceebeb191
Reviewed-on: https://review.haiku-os.org/c/haiku/+/5937
Reviewed-by: Adrien Destugues <pulkomandy@pulkomandy.tk>