This commit introduces the extension modes to the corner pin node and
further streamlines the node properties by wrapping all props in the node
storage. Therefore, the interpolation mode has been removed from the
custom properties of the node and moved into the node storage.
Right now, the extension modes only work for non-anisotropic filtering.
Pull Request: https://projects.blender.org/blender/blender/pulls/141570
570f44a059