ShadowedImage: Fix rendering image
ShadowedTexture can't use an invisible item, it seems. So let's remove
it from hierarchy chain instead. It fixes images in Kirigami Gallery.
However, now it produces these warnings:
QQuickImage::textureProvider: can only be queried on the rendering thread of an exposed window
ShadowedTexture can't use an invisible item. So let's use a proxy ShaderEffectSource which can hide its source item instead.
It fixes images in Kirigami Gallery.
Edited by ivan tkachenko