...revert to previous change, since always calling the constructor of
VersionedData may have unintended consequences. Instead, just set .converts and
._encoding, since they are no longer in the prototype and must be set on the
object itself.
Creating SINs was broken due to not calling the parent constructor, shich sets
"converts" and "_encoding". I've fixed the problem and added tests that reveal
the error.
EncodedData was setting "converter" and "_encoding" by setting them on the
prototype of the object. This was probably done to enable overriding these
functions. However, overriding was never actually used anywhere, and setting
the __proto__ is deprecated. So I have remove all instances of setting
__proto__ for EncodedData-ish classes, and instead just set "convert" and
"_encoding" on the object directly.