Effects support in Qt6

Currently the effects story is two-fold and does not have full Qt6 support. On the other hand we have Qt Graphical Effects that is supported with limited functionality via Qt5 compat library but not using Qt6 full feartures like RHI support or shader tools.

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Then we have Multieffects which is a component in Marketplace but does not even have proper support from the RND -- and it's not even a real module.

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To unify this story we need to have one package that combines benefits from both of these packages and includes support from Qt Design Studio.

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Update: We are aligning basic postprocessing effects so they match Figma offering. In addition to this, we are ramping down multieffects package and bring effect maker with proper integration to Qt Design Studio.

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