Does not compile for certain Qt versions due to missing modules

[celerizer]

The required multimedia module is not available for Qt versions 6.0-6.2 and the required gamepad module is not available for any version of Qt 6, causing compilation to fail for Qt 6.

QRetroAudio and QRetroMicrophone should have compile-time settings to disable most of their behavior, as QAudioOutput and QAudioInput are part of the multimedia module.

QRetroInput should be created and the code should be moved out of QRetro.cpp. QGamepad should also be skipped in compilation if the gamepad module is unavailable. A new default gamepad implementation may be out of scope for the project, but there should be a default method for controlling libretro joypads on Qt 6, even if only with the keyboard

[celerizer]

With 38a3f18 the gamepad module is now no longer required, but the multimedia module still is