QAbstractItemView should forward mouse click for some editors when SelectedClicked is the edit trigger

Ie. when having a QComboBox as the editor widget in the delegate, then right now it requires three clicks to open the combobox popup for any unselected cell:

• select the cell
• click on the selected cell (and wait for the double click timeout)
• open the popup

This is not very efficient, and having CurrentChanged as an edit-trigger is not always desireable (and the "current" might not change).