Since you can already specify a separate size for X and Y with the
grid node, it makes sense to be able to specify the size separately
for each axis also.
This also avoids some awkward math with a Transform node afterwards
when you want a specific size for each direction.
Versioning (except for animation and drivers) is handled in this commit.
Differential Revision: https://developer.blender.org/D10834
46d75052eb