RHI Quick3D: Further work on post-processing effects

The core functionality of the Effects system was ported to RHI in QTBUG-82247. This task lists identified remaining or potential tasks:

• Make effects work for other rendermodes than Offscreen QTBUG-99698
• MacOS/metal: Effects using depth buffer do not work, e.g. lancelot test scenes abberration.qml and depth.qml [DONE]
• MacOS/metal: TiltShift and MotionBlur do not work, ref. effects/move.qml and effects/misc.qml {DONE]
• The predefined texture pngs in src/imports/effectlib/maps are not found after install. They should anyway not need to be distributed separately, but should be turned into resources instead [DONE]
• The effect qml files and pngs, are installed/distributed both as resources in the lib and as separate files. If not intentional, should be cleaned up after qmake purge [DONE]
• Performance optimization. Compare performance with directGL path. Possibly potential for caching resources between frames. Ref. QTBUG-83706. [DONE]
• Merge better with AA; utilize effect system to implement some of the AA, to avoid code duplication [WONT DO]
• Implement remaining Commands? Only the commands actually used in the effectlib have been implemented so far. Nope, ref. https://codereview.qt-project.org/c/qt/qtquick3d/+/306423
• Research the "active" state of effects, and implement if needed. [DONE, dropped]
• Research and fix as necessary the need for texture/buffer premultiply and the setting of the "mix" uniform, ref. https://codereview.qt-project.org/c/qt/qtquick3d/+/296900 and https://codereview.qt-project.org/c/qt/qtquick3d/+/297324. [DONE]
• Fix crash when a texture property ends up empty, e.g. by referring to a non-existent file [DONE]
• Sort out effect orientation vs. rhi backend issues so the result is the same for all backends: QTBUG-83812
• Sort out texture property vs. rhi backend issue on vulkan, a texture property from file ends up flipped compared to opengl (variant of previous item)
• Texture properties like scaleU/V etc. have no effect [DONE, documented behavior]