Changed Select Grouped operator to operate on whole selection

Right now the Select Grouped object operator only considers the active object, not the whole selection. So if I want to select multiple objects in different collections and want to select all other objects in their respective collections.

Making this change should be possible without an additional object to switch between active/selection as the cases where users only want this to operate on the active object would probably be very rare.

This would also make the operator consistent with the Select Similar operator in Edit Mode which is very similar.