try sdl3

[briaguya0]

things that are working:

• gets in game from my linux dev env

things that still need to happen:

• we need to bump imgui - the sdl3 backend for the version we have in dev doesn't have all the sdl3 changes we need. i pulled in imgui 1.90.6 -> 1.91.6 #4738 for this but that is basically just a proof-of-concept and not fit to land. i think bumping imgui to the latest docking release should be a prerequisite and land before we try to bump to sdl3.
• get this working in windows and mac dev envs
• get this building in ci
• quite a few todos (see my self-review on the lus pr)
• testing

related:

• try sdl3 ZAPDTR#28
• try sdl3 Kenix3/libultraship#783

Build Artifacts

[briaguya0]

this was discovery, closing in favor of #4859