Expose init data, local init and client context in DuckDB::TableFunction #1540

Split from #1123.

Remaining user-facing APIs:

• InitInfo#init_data= — wrap duckdb_init_set_init_data
• FunctionInfo#init_data — wrap duckdb_function_get_init_data
• TableFunction#local_init + FunctionInfo#local_init_data — duckdb_table_function_set_local_init / duckdb_function_get_local_init_data are currently used internally for the worker proxy (DuckDB >= 1.5.0), so a user-facing API must coexist with that
• BindInfo#client_context — wrap duckdb_table_function_get_client_context