Add JSON_DECODE() function to decode a json string to a dynamic column structure

Dynamic column functionality includes a COLUMN_JSON() function to transform a dynamic column structure to a JSON string. It would be handy to also have a counterpart function that decodes a JSON string into a dynamic column structure. It could potentially be used like this

SELECT COLUMN_GET(JSON_DECODE('{"child_column":12345}'), 'child_column' AS int);

SELECT COLUMN_GET(COLUMN_GET(JSON_DECODE('{"parent_column":{"child_column":12345}}'), 'parent_column' AS char), 'child_column' AS int);

I currently store quite some JSON values as TEXT in tables, so alternatively this could also allow me to use JSON_DECODE() on INSERT to store it as a dynamic column structure directly.