Port 2D improvements to move and slide 3D (with extras)

[fabriceci]

Thanks to @pouleyKetchoupp for his help/work on this, as this was harder than I thought. The latest "jitters" are definitively the worst :)

fix #30310
fix #50756
fix #51874
fix #52887

Test project: https://github.com/fabriceci/3d-platform-test-for-godot4 (based on the @TokageItLab one, thanks to him)

This PR should provide a good physics by default for CharacterBody3D, without any effort.

• all the improvement added in 2D to move and slide + new improvement (ability to choice the behaviour when the body left a platform)

• the ability to detect multiple collisions on move_and_collide which allows us to handle advanced cases like the one below in the screenshot when the body is stuck between two walls

• new methods to retrieve important information (latest motion, true velocity, etc.)
• tweak value/code to behave nicely by default: minimal floor snap, default floor snap, etc.

[pouleyKetchoupp]

Great work! I've left some comments about details but it generally looks good.

Edit: Also needs a rebase because of recent changes in the documentation.