This PR fixes https://github.com/duckdblabs/duckdb-internal/issues/155

This should improve the error message that users gets when they are misusing a function that lives in an extension.
For example, the provided test:

statement error
FROM json("['item':'phasers','year':2155','count':1035]");
----
Catalog Error: Table Function with name "json" is not in the catalog, a function by this name exists in the json extension, but it's of a different type, namely Macro Function

I also took the opportunity to clean up the scripts/generate_extensions_function.py that we use to generate this file
It should be much more trivial and straightforward to extend this script to the other remaining catalog entries of extensions.