Add wxUiEditor/codegen forms to tests.

Description:

Now that the wxWidgets source files for wxUiEditor are retrieved via CMake's FetchContent, the wxUiEditor/codegen test doesn't work. For the most part, it duplicates the testing in the wxUiTesting repository. In theory, that could be run as a github action, but it would add a significant amount of time to the build. It is, however, quite straightforward to run it as a task from a wxUiEditor code session.

There are some stand-alone forms that were added to codegen. These should be added to wxUiTesting as well, even though they aren't actually used in the application itself. Having them there will still compile them for C++, and syntax check them for Perl, Python, and Ruby.