MacOS: Raw mouse motion and cursor grab

[Deseteral]

When not-fl3/macroquad#181 added support for raw mouse motion events in macroquad it didn't work on MacOS because of missing set_cursor_grab implementation for that plaform. This PR adds support for missing MacOS features.

My work is based on current implementation of mouse locking in sokol_app.

It uses CGAssociateMouseAndMouseCursorPosition to lock the cursor and CGWarpMouseCursorPosition to move it inside window frame (more on this later). When the cursor is grabbed and mouseMoved is emitted we're calling raw_mouse_motion with deltaX and deltaY values.

One notable difference from sokol is that in my implementation when user calls set_cursor_grab(true) I'm moving the cursor inside window frame. Without this when the cursor is outside window frame when the set_cursor_grab is called, a mouse click will unfocus the window.

Moving the cursor inside window frame is what sokol_app used to do, but it does not anymore, which is explained in their code:

NOTE that this code doesn't warp the mouse cursor to the window center as everybody else does it. This lead to a spike in the second mouse-moved event after the warp happened. The mouse centering doesn't seem to be required (mouse-moved events are reported correctly even when the cursor is at an edge of the screen).

This is what that spike looks like in macroquad (using miniquad from this branch):

macroquad_mouse_twitch_e.mov

In my opinion we should follow what sokol does. Most games are probably fullscreen anyway and when they're not - users will click on the window to focus. On the other hand this is still going to be a problem when users alt-tab to the window.

Let me know what you want to do about it - we can leave it as it is, or I will remove moving the cursor.

I've tested this change with all miniquad examples, and most importantly with macroquads first_person example (as seen on video below).

macroquad_example_e.mp4

If there is something specific you would like me to test - let me know.

[not-fl3]

Thanks, great PR!

Let me know what you want to do about it - we can leave it as it is, or I will remove moving the cursor.

The behaviour you described sounds very reasonable to me, but to be honest, I do not have an opinion here.

[Deseteral]

Thank you for that incredibly fast review 😄