bgfx update

[belegdol]

Hello,

there have been some Wayland improvements to bgfx upstream recently:

• bkaradzic/bgfx@3303b45
• bkaradzic/bgfx@a6e372e
• bkaradzic/bgfx@e488a07

I would like to get them added to mame as they fix the surprisingly well functioning guesswork I submitted last year. Last year we ended up cherry-picking changes needed to get Wayland working because simple syncing broke compatibility with older macOS versions, among others [1]. I could try cherry-picking the new updates too, but this will lead to more merge conflicts once we actually do want to sync with upstream. This would not be the case if we did sync.
What is the oldest macOS version we care about as of today? And would anyone be willing to test a build on it? Thanks for the input in advance.
For reference, bgfx supports macOS 13 and above.

[1] mamedev/mame#11493