add support for databricks JSON accessors

[whirlun]

Support databricks SQL JSON accessors
sample queries:

SELECT c1:price
    FROM VALUES('{ "price": 5 }') AS T(c1);
 SELECT c1:['price']::decimal(5,2)
    FROM VALUES('{ "price": 5 }') AS T(c1);
SELECT c1:item[1].price::double
    FROM VALUES('{ "item": [ { "model" : "basic", "price" : 6.12 },
                             { "model" : "medium", "price" : 9.24 } ] }') AS T(c1);

spec: https://docs.databricks.com/en/sql/language-manual/functions/colonsign.html

the tests are written by Claude Code because it can write tests magnitudes better than me.

[iffyio]

LGTM! Thanks @whirlun!