SQL Server: use the new modify method for partial update on the json type

[roji]

Our update pipeline currently uses JSON_MODIFY() to perform partial updates inside JSON documents. SQL Server 2025 is introducing a new modify method that can do the same in a more efficient way (docs).

Note that partial updates aren't yet implemented for complex JSON, only owned (#36429), though this is orthogonal.

/cc @AndriySvyryd