Add support for legacy input system buttons and key down in Dialogue Advance Input

[ketexon]

Problem

With the classic input system, Dialogue Advance Input only allows input via keycode, not buttons (ie. Input.GetButtonDown), and only allows checking for key release, not key down. The latter is an actual bug if the button used for selecting an option is the same as the button for advancing input, as this will cause the option to be selected on key down and then the input advanced in key up.

Solution

Adding support for virtual buttons and adding a field for whether the keycode/virtual button should trigger the advancement on button down or button up.

[ketexon]

I can work on this if it a desired feature