JSON Path computation doesn't do lax mode unboxing

Filing this not because I expect we will fix this [soon], but rather to document this limitation.

MariaDB supports "lax mode" for JSON Path evaluation. SQL Standard specifies that in this mode the JSON Path evaluator provides "boxing" and "unboxing" - ignoring one-element arrays when we don't expect them and pretending there is one when JSON document doesn't have it.

Should we care about this here?
It seems not: MariaDB follows MySQL and provides non-standard behavior!
Example:

SELECT JSON_VALUE('{"user": [{"name": "Alice"}]}', '$.user.name') AS extracted_name

FROM DUAL;

This returns NULL in both MariaDB and MySQL.
In OracleDB, it returns "Alice" (https://sqlfiddle.com/oracle/online-compiler?id=df76eb6b-bb8d-46e8-a164-3ca92bfcd2f4)
In PostgreSQL,

SELECT jsonb_path_query('{"user": [{"name": "Alice"}]}', '$.user.name');

also returns "Alice".

This was also discussed, especially w.r.t. mongodb, in https://jira.mariadb.org/browse/MDEV-37288?focusedCommentId=310846&page=com.atlassian.jira.plugin.system.issuetabpanels%3Acomment-tabpanel#comment-310846

More specifically, the unboxing could happen anywhere along the path, as https://www.mongodb.com/docs/manual/core/indexes/index-types/index-multikey/create-multikey-index-embedded/#std-label-index-create-multikey-embedded shows. This means for

set @j = '{

  "item": "t-shirt",

  "stock": [

    {

      "size": "small",

      "quantity": 8

    },

    {

      "size": "large",

      "quantity": 10

    }

   ]

}';

one could get something like json_extract(@j, '$.stock.quantity') = 8 to evaluate to true.