[PropertyOverrideButton] fire modfiication signals on setToProperty

[troopa81]

Fixed during #64877

No AI usage

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[nyalldawson]

@troopa81 this potentially introduces update loops (eg a widget listening to changed signals on the button, then an "update state" method in that widget setting the button GUI to match, which the triggers and unwanted "changed" signal from the widget (when nothing actually was changed by the user)

It's usually cleaner to make the caller responsible for handling this, and not relying on API setting of button state to trigger a different slot. Just call that manually from the code setting the button state instead.

Otherwise you'd need to do a full check over everywhere these signals are connected and setToProperty is called, to verify that there's no chance of regression. (And that's a LOT of places)