Combine vsc-lib and ifex tools (ifex_ast)

[gunnarx]

This work is being done in #31
The idea is to provide convience functions to create nodes in a VSC tree. This is what vsclib does. It also does a few other things like checking if a mentioned typedef can be found, following namespace/scoping rules.

Now that the implementation defines the language in one specific file: vsc_ast.py, the vsc-lib should be rewritten to use that exact definition.

• One way is to import vsc_ast and add functions that return such types. This keeps the vsc_ast classes as pure dataclasses. (They have the information but not any operations)
• Another way is to provide operations inside the classes. This is a more traditional OO approach, to provide data and the operations combined in a class, but it will add a lot more text to vsc_ast.py so it will be less readable as a kind of "specification" of the language.