qml: use QSGTextureView (TextureProviderItem) in PartialEffect instead of layering

We already have the source texture (dynamic texture),
because the source is layered. Currently we are using
layering again for applying effect in the area denoted
by effect rect, however we don't need to do that.

With QSGTextureView, we can simply use the area denoted
by effect rect, without layering (thus additional frame
buffer object).