Add fromJsonBytesWithType to lang.value

[jclark]

Might be useful to add

public isolated function fromJsonBytesWithType(byte[] bytes, typedesc<anydata> t = <>)
    returns t|error = external;

to lang.value. This would be a combo of string:fromBytes and value:fromJsonStringWithType except that it should support (and automatically recognize) UTF-16 and UTF-32, which, together with UTF-8 are the only encodings of JSON allowed by RFC7159.