`changedAny` and `changedOnly` functions

[saiichihashimoto]

The groq spec and the sanity docs both mention the changedAny() and changedOnly() functions, but groq-js doesn't support them yet.

[judofyr]

Yup, it would be nice to have these. It's just been deprioritized since they are rarely used in queries on the client-side.