Many functions are missing override or final specifier

After the introduction of the override and final specifiers in C++, Qt Creator's code base slowly adapted the habit to use override or final on function level and final on class level.

Running clang-tidy with the modernize-use-override reveals that many overridden virtual functions are either without any specifier or still (redundantly) specified as virtual.

See the diff after a clang-tidy run: https://codereview.qt-project.org/c/qt-creator/qt-creator/+/304301