Transfer whole sequence to backend

Qt supports Emacs-style key sequences, with up to four key codes.

Using int, only first key code was passed to backend which leads the user defined sequence to silently crop.

Thus, we need to implement the following checks:

1. Compare sequences for equality

2. Compare sequences for overlapping e.g. Alt+A,Alt+B overlaps Alt+A,Alt+B,Alt+C causing latter to never being triggered.

   Also we need to check if the keys are being used when a shortcut is reset. e.g. we don't need to ungrab Alt+X if there are other sequences with Alt+X.

   Along with this patch, kdeclarative changes are required.

[1] https://doc.qt.io/qt-5/qkeysequence.html#count

BUG: 442079

Dependent MR: kdeclarative!81 (merged) kxmlgui!85 (diffs) plasma/plasma-desktop!726 (merged)