RNA: rename prop_popover_enum to prop_with_popover

A version for menu's is going to be added next and we already have
UILayout.prop_menu_enum.

This name indicates the popover is added behavior instead of a
different kind of widget.

source/blender/editors/interface/interface_layout.c

@@ -2003,7 +2003,7 @@ void uiItemFullR_with_popover(
 	but = but->next;
 	while (but) {
 		if (but->rnaprop == prop && but->type == UI_BTYPE_MENU) {
-			ui_but_rna_menu_convert_to_popover(but, panel_type);
+			ui_but_rna_menu_convert_to_panel_type(but, panel_type);
 			break;
 		}
 		but = but->next;