Add new QtQuick.Effects plugin for post-processing effects. The plan is to add essential effects directly into QtQuick, not to duplicate Qt Graphical Effects. Initially the plugin will contain MultiEffect which supports 7 different effects in a single ShaderEffect (brightness, contrast, saturation, colorize, blur, shadow, mask). Combining multiple effects into a single shader is more performant than chaining multiple effect items. Depending on used features, the most optimal shader gets selected. Includes two examples demonstrating the usage of MultiEffect. Task-number: QTBUG-106651 Change-Id: I35865030fd4b7a1f657146cee03b195451545bc6 Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@qt.io>