Update to mGBA 0.10.3

[WingofaGriffin]

https://mgba.io/2024/01/07/mgba-0.10.3/

Differences between versions: mgba-emu/mgba@0.10.2...0.10.3

[ketsuban]

mGBA has since updated to 0.10.5 (release post, changelog, diff) doubling the backlog of commits to transfer over.

[wblondel]

OpenEmu seems abandonned. The latest commit was over a year ago.