[Feature] Option to center split and modern HUDs

[sinisterseed]

Based on the later discussions from #447 .

I believe a fair point can be made here about centered HUDs, notably for ultrawide/21:9 screens as they are considerably wider than 16:9 and the partial and modern HUDs would be so far away on the edges of the screen on those.

Being able to center these HUDs would surely be beneficial for them.

[mjr4077au]

Perhaps a "HUD Aspect Ratio" option to set it to 5:4, 4:3, 16:10, 16:9, 21:9 and 32:9 or screen's aspect as appropriate could be ideal?

[sinisterseed]

Ideal, yes, surely. How feasible? That remains to be seen.

[Calinou]

I think the ideal way to fix this is to add HUD margin options, so you can adjust both horizontal and vertical margins. This can also be used to fix the HUD being "eaten" by overscan on certain monitors/TVs.

If you just set a non-zero horizontal margin, this can be used to constrain the HUD to a specific aspect ratio manually.