Enable easy transform baking via GeometryUtils.bakeObjectTransformIntoGeometry().

This is a useful function and it was hidden inside TransformControls.js

Alternative names for this function:
* ```GeometryUtils.bakeTransform( object )```, but I wanted it to be clear this operated on object and backed the transform into the geometry.
* ```Object3D.bakeTransform()```, nice location but the issue is that this function requires a geometry to work properly, so I thought putting it here could lead to issues.

Baking of transforms is frequently used in preparing assets for games and also for creating complex objects that share a single origin (such as the TransformControl.)

It is best to have this in a central location were we can ensure that it is correct.