CloudKit JS' support for encrypted fields

[sophiebremer]

During debugging of CloudKit JS typing of RecordField, I discovered a fragmented support for encrypted fields. This is not part of the CloudKit JS documentation, but the library does support at least a fraction of encrypted fields:

• Receiving encrypted record fields is transparent for all types, so that the value gets decrypted and RecordField.isEncrypted = true.
• Sending encrypted record fields is limited and mostly hidden. It looks like only 'ENCRYPTED_BYTES' is supported by the client library, while the server API also supports other types like 'ENCRYPTED_STRING'.

The regular documentation describes the feature in detail: https://developer.apple.com/documentation/cloudkit/encrypting_user_data

Some form of support could be added to tsl-apple-cloudkit, if there is enough interest.