Bounce calculation now uses the previous frame's velocity, so it's
consistent with the actual motion of the bodies involved and not the
yet-to-be-applied forces.
When bounce is 1, using the current velocity was causing the new forces
(including gravity) to be taken into account, which lead to the bounce
velocity to be higher than the falling velocity at the moment of impact,
adding more and more energy over time.
Center of mass in body's local space is more useful than the transformed
one in some cases, like drawing its position for debug.
It's especially useful to get the generated local center of mass when
in auto mode (by default).
Physics Server BODY_PARAM_CENTER_OF_MASS:
Now always returns the local center of mass, instead of setting a local
center of mass and getting a transformed one.
This causes compatibility breaking, but it makes more sense for the
parameter to be consistent between getter and setter.
Direct Body State:
There are now two properties, because both of them can be useful in
different situations.
center_of_mass: relative position in global coordinates (same as before)
center_of_mass_local: position in local coordinates
Damping values are now non-negative.
Add new properties linear_damp_mode and angular_damp_mode to set the way
RigidDynamicBody and PhysicalBone (2D & 3D) use damping values.
It can now be Combine (default) to add to the default/areas, or Replace
to override the value completely (current behavior).
Same logic as what was done in 3D, applied to 2D center of mass.
Also did some minor cleanup in 3D and fixed center of mass transform
during the first frame after teleporting a dynamic body.
