py_wrap: implement nested class definitions

[widlarizer]

Fixes #4670 by probably implementing nested class declaration. I don't really know what the wrapper generator does and I don't want to find out more than I already did. Also the DIY C++ parser doesn't like trailing commas in enum declarations so I removed it from RTLIL::ConstFlags.

[povik]

Is there a diff in the generator's output against what it produced the last time it worked?

[widlarizer]

Here you go. The diff is the const additions and then temporary variable naming noise

python_wrappersnew.txt
python_wrappersold.txt

[povik]

The flags property seems to have disappeared

[widlarizer]

short -> short int fixes that

[povik]

Not the change I expected to help

[povik]

The generator output looks good so I think we can merge this