Replace "Show FPS" effect with a QML version

This removes a bunch of custom rendering, replacing it with a simple QML file that makes use of KQuickCharts for chart rendering. Functionally, it should be mostly the same except that I removed all configuration options as I don't see why we have those.

This was done because while working on !2739 (merged) I found it really hard to follow the old code and making simple changes broke the entire thing.