Consider to split GitHub Actions according to the generators

[mikir]

Currently, we have one GitHub action for Linux (build_linux.yml) and one for Windows (build_windows.yml). These actions take too long and we have already hit the 6-hours limit (see commented out job 'Run Zserio tests with extra arguments (Debug Build)').

It would be probably better to split these actions according to the generators (C++, Java, Python, Doc, XML).