PhysicsMaterial needs better documentation for friction and bounce

[pouleyKetchoupp]

Godot version:
3.3 stable / Master

OS/device including version:
Any

Issue description:
Following up on #48434 (comment).

The documentation states friction and bounce are in the interval 0..1 from no effect to full effect:

godot/doc/classes/PhysicsMaterial.xml

Lines 17 to 22 in e189ff5

	<member name="bounce" type="float" setter="set_bounce" getter="get_bounce" default="0.0">
	The body's bounciness. Values range from [code]0[/code] (no bounce) to [code]1[/code] (full bounciness).
	</member>
	<member name="friction" type="float" setter="set_friction" getter="get_friction" default="1.0">
	The body's friction. Values range from [code]0[/code] (frictionless) to [code]1[/code] (maximum friction).
	</member>

But in practice higher values can be needed in some cases and the effect in physics in not very clear.
See #48298

The effect of friction and bounce needs to be investigated, and compared between Godot Physics 2D/3D and Bullet, and the documentation needs to be updated with more accurate information.

Steps to reproduce:
n/a

Minimal reproduction project:
n/a