Currently, scaling doesn't work correctly on macOS (see #5185). This commit
works around this issue by disabling SCALE_FRAMEBUFFER on macOS when
`FLAG_WINDOW_HIGHDPI` is unset.
* fix definition to use SDL3
* [cmake] fix definition to use SDL3
* [build][cmake] prefer USING_VERSION_SDL3 over PLATFORM_DESKTOP_SDL3
* [build][cmake] when libs are added externally, consumer needs to import them too