INT: the json C code should not deal with blocks
PR https://github.com/pandas-dev/pandas/pull/26409 introduced a `get_block_values` to get the values of the Block, used in https://github.com/pandas-dev/pandas/blob/master/pandas/_libs/src/ujson/python/objToJSON.c

Ideally, the JSON C code should not deal with blocks (eg by converting to a numpy array before passing the data to the C code).

So to do item for this issue: update the JSON code so the call from objToJSON.c to `get_block_values` can be removed.