`Canvas::get_pixel`: Use a virtual colorspace

[Vankata453]

Virtual colorspaces, consisting of colored shapes, can now be used for the get_pixel API, instead of relying on the GPU.

TODO:

• [x] Detect, or allow to specify lightsprites as circles with a radius and border radius, making the light check more visually correct.
• [ ] Divide Spotlight light sprite into two and draw them separately, to achieve a more exact light check by specifying a circle radius for each.
• [ ] Make sure the shape of every lightsprite, needed to be detected by the get_pixel API, is being added into the LIGHTSPRITES colorspace.
• [ ] More extensive testing.

Fixes #2661. Fixes #1939 (theoretically, should also be tested).