Fix windows build.

[zardoru]

This PR removes the old SDL2 dependencies and updates them to SDL3, plus fixes some source code references and removes the now-removed Action.c. It compiles correctly. I haven't been able to test much beyond that.

Oh yeah, also, to reflect the structure of how you download the libraries from SDL3 (which have lib and include directories) the include structure has been changed to be closer to that.