Support additional @transform()'s

[u9g]

• [ ] Ability to @transform(op: "split", value: ["$split_with_string"]) on strings.
• [ ] Ability to @transform(op: "join", value: ["$join_with_string"]) on string arrays.
• [ ] Ability to @transform(op: "add", value: ["$x"]) on numbers

[u9g]

Main blocker is that @transform in it’s current form doesn’t accept options