Various performance improvements for FrameSvg and PlasmaComponets3 Button

Merged Arjen Hiemstra requested to merge work/ahiemstra/framesvgperf into master

PC3's Button is pretty heavy to create, according to the QML profiler somewhere between 2.5 to 5ms, compared to roughly 1ms for QtQuick Control's Button with the default style.

To improve this, this MR contains a number of commits that attempt to improve the performance of this.

Draft because I have more pending changes.

Edited by Arjen Hiemstra

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