Feature: Native FlatGeobuf copy/table function

FlatGeobuf is a great and fast alternative to GeoJSON that's becoming more and more prevalent.
We should be able to use the generated c++ code to implement a single-threaded table/copy function relatively easy.
Since flatbuffers is a relatively simple format, a potential optimization would be to look into creating a zero-copy scanner that doesn't have to materialise any of the structs provided by the codegen.