Refactor!: improve transpilation of JSON paths across dialects

[georgesittas]

Fixes #2839, still a WIP; opening for some feedback

References:

• https://cloud.google.com/bigquery/docs/reference/standard-sql/json_functions#json_extract
• https://duckdb.org/docs/extensions/json.html
• https://dev.mysql.com/doc/refman/8.0/en/json-search-functions.html
• http://prestodb.io/docs/0.284/functions/json.html
• https://www.postgresql.org/docs/9.3/functions-json.html
• https://docs.aws.amazon.com/redshift/latest/dg/JSON_EXTRACT_PATH_TEXT.html
• https://docs.snowflake.com/en/sql-reference/functions/json_extract_path_text
• https://learn.microsoft.com/en-us/sql/relational-databases/json/validate-query-and-change-json-data-with-built-in-functions-sql-server?view=sql-server-ver16#JSONCompare
• https://www.sqlite.org/json1.html#jex

[georgesittas]

A possible improvement is to consolidate multiple -> or ->> applications into a single JSONExtract node by merging the respective JSON paths, but I'm thinking to leave it for a future PR. Right now we parse these chained operations into multiple JSONExtract nodes:

>>> import sqlglot
>>> sqlglot.parse_one("x -> 'a' -> 'b' -> 'z'", "postgres")
JSONExtract(
  this=JSONExtract(
    this=JSONExtract(
      this=Column(
        this=Identifier(this=x, quoted=False)),
      expression=JSONPath(
        this=[
          {'kind': 'root'},
          {'kind': 'key', 'value': 'a'}])),
    expression=JSONPath(
      this=[
        {'kind': 'root'},
        {'kind': 'key', 'value': 'b'}])),
  expression=JSONPath(
    this=[
      {'kind': 'root'},
      {'kind': 'key', 'value': 'z'}]))
>>> sqlglot.parse_one("x -> 'a' -> 'b' -> 'z'", "postgres").sql("bigquery")
"JSON_EXTRACT(JSON_EXTRACT(JSON_EXTRACT(x, '$.a'), '$.b'), '$.z')"
>>> sqlglot.parse_one("x -> 'a' -> 'b' -> 'z'", "postgres").sql("duckdb")
"x -> '$.a' -> '$.b' -> '$.z'"

[georgesittas]

FYI the only remaining dialect I need to refactor is Snowflake, but their path syntax is a bit weirder than the rest of the dialects that don't support the JSON path syntax as-is. DuckDB doesn't support the full spec of JSON path too and they seem to have augmented the path syntax with their own, for example the # here is not in the official spec:

SELECT json_extract('{"duck": [1, 2, 3]}', '$.duck[#-1]');

Refer to the linked docs for more info. You can also have JSON Pointer syntax for DuckDB paths which will be left as-is.