Add new json functions from datafusion-functions-json

[mwylde]

Adds additional json functions, from https://github.com/datafusion-contrib/datafusion-functions-json:

• json_contains(json: str, *keys: str | int) -> bool
• json_get(json: str, *keys: str | int) -> JsonUnion
• json_get_str(json: str, *keys: str | int) -> str
• json_get_int(json: str, *keys: str | int) -> int
• json_get_float(json: str, *keys: str | int) -> float
• json_get_bool(json: str, *keys: str | int) -> bool
• json_get_json(json: str, *keys: str | int) -> str
• json_length(json: str, *keys: str | int) -> int

These should be much faster (and a bit easier to use) than our existing JSON functions, albeit less powerful. In particular, using them with arrays of objects isn't yet possible.