Sketcher: [skip ci] Fix several clazy issues:

* Missing reference in range-for with non trivial type [-Wclazy-range-loop-reference]
* Unused QString [-Wclazy-unused-non-trivial-variable]
* Missing emit keyword on signal call [-Wclazy-incorrect-emit]
* Don't call QList::operator[]() on temporary [-Wclazy-detaching-temporary]
* Use multi-arg instead [-Wclazy-qstring-arg]
* Maybe you meant to call ViewProvider2DObjectGrid::onChanged() instead [-Wclazy-skipped-base-method]

src/Mod/Sketcher/Gui/EditDatumDialog.cpp

@@ -244,7 +244,7 @@ void EditDatumDialog::drivingToggled(bool state)
 
 void EditDatumDialog::datumChanged()
 {
-    if (ui_ins_datum->labelEdit->text() != ui_ins_datum->labelEdit->getHistory()[0]) {
+    if (ui_ins_datum->labelEdit->text() != qAsConst(ui_ins_datum->labelEdit)->getHistory()[0]) {
         ui_ins_datum->cbDriving->setChecked(false);
     }
 }