Port codebase over to SDL3

[loudbytes]

Important changes:

• Added setRelativeMouseMode to Window class as the RelativeMouseMode function is now linked to the window in SDL3. The original function in Engine remains, it simply calls the one in Window.
• MouseMotionEvent and MouseWheelEvent now use floats instead of int32s.
• Remove handleWindowEvent from the Window class. This was a private method already so the ergonomics haven't changed and the code readability hasn't been impacted because both functions affected were already small. This is because the SDL_WINDOWEVENT event type doesn't exist anymore, and to check if its a window event you need to check if the event type is within a range. Instead of adding an additional if check, I deemed it preferable to move the switch case from handleWindowEvent to the handle method instead as it only had 3 cases.

None of these changes should introduce regressions and the project builds correctly on my system. It currently does not run because of an issue with GLEW, but Synchro has a PR lined up to swap over to GLAD instead, which is better supported and should fix the issue.

[modawan]

Perfect, thank you very much!
Checked on my machine with SDL3 built from source (release-3.4.0) - engine, toolkit, imgui branch all work well. Checked on Windows with both SDL3 and GLAD changes - also no regressions.