26645: Fixed Undo/Redo buttons' hover state when disabled

[krasko78]

Resolves: #26645

Key points:

1. Added && root.enabled to the condition for the "HOVERED" state.
2. Did the same for the "PRESSED" state for consistency although it wasn't needed for this issue.
3. Removed enabled: root.enabled from the MouseArea since it has side effects. See below.
4. As a consequence of 3. I also added && root.enabled to the tooltip display so it does not appear when the button is disabled which is the current behavior although there is a story to re-enable tooltips for disabled elements: Make disabled buttons focusable & show their tooltips on hover #26232

Disabling the MouseArea together with the button has side effects when the button is disabled upon its own click. This is the case with the Undo and Redo buttons when there are no more actions to undo/redo. In particular containsMouse of the MouseArea remains true when the button and its MouseArea get disabled. This means that the "HOVERED" state will remain active. This could be worked around by adding && mouseArea.enabled to the condition of the "HOVERED" state.

However, there is more: containsMouse will continue to be true even if the mouse then leaves the now disabled button. Let's say this is the Undo button and it becomes disabled on click since there are no more actions to undo. The user moves the mouse away from it and over the Redo button. containsMouse of the Undo button's MouseArea continues to be true since both the button and the MouseArea are now disabled and the MouseArea does not react to any mouse events any more. If the Redo button is now clicked, this will re-enable the Undo button and its MouseArea. The Undo button's "HOVERED" state will fire even though the mouse is hovering the Redo button.

The conclusion for me is we should not be disabling the MouseArea. Instead we should be checking root.Enabled where necessary. Again, #26232 is probably another reason to not disable the MouseAreas. The disabling of the MouseArea-s was done for #25697.

@cbjeukendrup What are your thoughts? Should we revert the disabling of all the MouseAreas and add '&& .enabled' where necessary? Or do you see a better approach?

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[cbjeukendrup]

Good research! By your explanation, I'm convinced that disabling the MouseAreas was indeed not the best idea, so I'd be okay with reverting that and solving #25697 differently. I also don't really see an alternative way.