VMU screen on a second/external display on Android #2123
Description
Is your feature request related to a problem? Please describe.
With the announcement and releases of several Android handhelds with two built-in screens, such as the Ayaneo Pocket DS, AYN Thor (I have this and demonstrating it below), Anbernic RG DS, and ONEXSUGAR Sugar-1, it just now occurred to me that the second screen/monitor could be used to display VMUs so they are not on the same screen as the gameplay screen/monitor, yet there is no option for that in the option menu. (And can the VMU screens be moved/dragged?)
Describe the solution you'd like
Adding an option in the Video settings to display the VMU screen on External Displays, with optional quality-of-life subfeatures like screen size options (pixel-perfect, integer-scaled, full non-stretched, and full stretched) for the VMU screen.
Describe alternatives you've considered
Emulators of 2-screen video game systems like Azahar and SapphireRhondite's dual screen forks of melonDS-Android and Cemu have managed to implement External Screen displays on Android, but they may be built differently than Flycast, so I wonder if it's possible or not to implement external screen functionality in Flycast for VMUs.
If it is possible, would it also be possible to move other notifications like the FPS Counter to the External Display?
Additional context
