made clear distinction between disabled and selected in sending signals.

[daBlesr]

I have made sure there is a clear distinction in which situations signals are triggered:

when item is disabled: send no signal at all for this item (activated, selected, deselected, ...) when item is selectable: send signals (item_selected, multi_selected) when not disabled.

when is activated now triggered? When item is not disabled and double clicked (pressing enter is only possible when selectable 😄 )

I am in conflict with deselecting however, I am allowing deselection even when selectable is turned off to keep this behaviour as before.

Fixes: #74086

[daBlesr]

Hi @KoBeWi could I request a review from you, or @akien-mga could you add anyone as a reviewer whom you might think would be able to review this PR?

[akien-mga]

OP was no longer responsive, so I went ahead and fixed the style issues myself.

[akien-mga]

Thanks!