Forward Alt and Super with SDK keyboard

Alt and Super (also named Meta) modifier keys are captured for shortcuts
by default (cf --shortcut-mod).

However, when shortcut modifiers are changed, Alt and Super should be
forwarded to the device. This is the case for AOA and UHID keyboards,
but it was not the case for SDK keyboard.

Fixes #5318 <https://github.com/Genymobile/scrcpy/issues/5318>
PR #5322 <https://github.com/Genymobile/scrcpy/pull/5322>