plugins: Make 'invert', 'zoom' and 'magnifier' internal, move config to Accessibility KCM

Oliver Beardrequested to merge
work/olib-tp/internal-invert-zoom into master

KWin part of plasma-desktop!2968 (merged).

These effects can be marked internal and we can drop their configuration here as the Accessibility KCM is now responsible for configuring them.

This MR also changes the default for the zoom effect scroll gesture modifier to "Control" as KeySequenceItem uses "Meta+Control" instead of "Meta+Ctrl", and the latter is recognised as invalid. We also need to interpret "Control" as "Ctrl". This is not done in X11 because it does not support the scroll gesture.

Edited by Oliver Beard

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