Wrap GDAL 3.0

[visr]

Now that we use the GDAL 3.0 library, we should rerun the wrappers under gen/ and bring the code back in sync with the libraries. IMO it would be best to do that before tagging a new release, as long as it doesn't take too long.

For adding the docstrings some work is needed anyway because of the Clang.jl changes. I'd like to see if we can make this code simpler via https://discourse.julialang.org/t/ann-automaticdocstrings-jl/24675.