Increase the KinematicBody default floor max angle to 46 degrees

Created by: Calinou

This makes 1:1 slopes considered as floors without having to override the parameter in the move_and_slide() methods.

This is of course a breaking change and shouldn't be cherry-picked into 3.2 🙂

This closes https://github.com/godotengine/godot-proposals/issues/402.