Add shapeAppearance and shapeAppearanceOverlay attributes. These attributes combine to support shapes theming. ShapeAppearance is modeled after TextAppearance. A shapeAppearance attribute contains a style reference that is meant to be defined at the theme level. Since changing anything defined in the shapeAppearance would clobber everything else in the ShapeAppearance, the shapeAppearanceOverlay attribute is provided for clients to modify the shapeAppearance.
PiperOrigin-RevId: 215242636
This commit renames ShapePathModel to ShapeAppearanceModel to align with the new shapeAppearance attributes that will be added for shape theming.
PiperOrigin-RevId: 214818189