Revert "#25241 Swapped init_engine() and _define_qt_base() call order. With this change, init_engine() is called after _define_qt_base(), making it easier for engines to do complex stuff in their init. Previously, init would be different than other code because QT was potentially not yet initialized. With this change, QT is fully initialized before init is called and init therefore can be expected to work in the same way as other callbacks and code with regard to QT."

This reverts commit 0512ef9ac5300032fc6b0495a650f0839d86eec8.