... if they are not set as actual binding before
As reported in #3068
The problem is that the pass will properly create the Rotation or
Opacity item, but will not create the two way binding if there is no
existing binding. This causes code like `img.rotation-angle = ...` to
change the rotation angle of the image, but not its parent Rotation
item.
Fix it by making sure there is always a binding.
Since the change only affect visual representation, I abused one of the
screenshot test to test this feature. And I also patched another bug
that some #[allow(unused_parens)] was not set in the 'init' callback and
would cause a warning in the test
The rotation-angle/rotation-origin-x/y properties are lowered to an
injected Rotate element, that we already had.
This needs further fixes for transforming input events and an
implementation of rotation in Skia.
