refactor: re-enable some clang-tidy checks in qt/ (#2585)

* chore: re-enable readability-static-accessed-through-instance test in qt

* chore: re-enable clang-diagnostic-nonportable-system-include-path check in qt/

* chore: re-enable clang-diagnostic-undefined-reinterpret-cast test in qt/

* chore: re-enable cert-err58-cpp check in qt/

* chore: re-enable clang-diagnostic-switch-enum check in qt/

* chore: re-enable modernize-return-braced-init-list check in qt/

* chore: re-enable cppcoreguidelines-pro-type-static-cast-downcast check in qt/

* chore: re-enable cppcoreguidelines-pro-type-cstyle-cast check in qt/

* refactor: re-enable cppcoreguidelines-init-variables check in qt/

* chore: re-enable cppcoreguidelines-pro-type-vararg check in qt/

* chore: remove explicit disable of clang-diagnostic-old-style-cast check in qt/

* chore: re-enable bugprone-implicit-widening-of-multiplication-result check in qt/

qt/PrefsDialog.cc

@@ -152,7 +152,7 @@ QString qtDayName(int day)
 
     default:
         assert(false && "Invalid day of week");
-        return QString();
+        return {};
     }
 }