[Feature Request] Proper Game Boy Camera/Game Boy Printer support

Description

While the separate apps for mGBA & Sameboy support the Game Boy Camera, and exporting Game Boy Printer printouts to a png file, this support doesn't exist in their RetroArch cores.

Expected behavior

Have the selected core register a camera and pass it to the Game Boy Camera rom to capture an image in-game. Also have an option to save the Game Boy Printer printouts to a png file somewhere. Possibly in the same rom directory like how screenshots are stored.

Actual behavior

mGBA:

A camera error message just appears shortly after loading the Game Boy Camera rom and then another error appears when trying to print an image via the Game Boy Printer.

Steps to reproduce the bugs

1. Open a Game Boy Camera rom
2. Wait a minute
3. See the error message
4. Try to print an image
5. See another error message

Sameboy:

When you try and take a picture, there's just a slightly glitched screen. No error message appears like in mGBA. If you try and print something, you see the usual print errors.

Steps to reproduce the bugs

1. Open a Game Boy Camera rom
2. Try to take a picture
3. See the glitched graphics
4. Try to print an image
5. See an error message

Bisect Results

It's been happening since I got an iPhone 13 Pro Max on release date.

Version/Commit

• RetroArch Build Date: Sep 19 2021

Environment information

• OS: iOS 15

Start by comparing the separate mGBA and SameBoy app support with the RetroArch core behavior described in the reproduction steps. Trace how the selected core could expose Game Boy Camera input and how Game Boy Printer output is handled. Done means the camera ROM can capture an image and printer output can be saved as a PNG.