Decoders (at least some of them) don't accumulate errors

[jisantuc]

Describe the bug
When you call decodeAccumulating on an empty json object for something with several fields, you should see several errors. Instead, this happens:

scala> decode[StacCollection]("""{}""")
res0: Either[io.circe.Error,com.azavea.stac4s.StacCollection] = Left(DecodingFailure(Attempt to decode value on failed cursor, List(DownField(type))))

scala> decodeAccumulating[StacCollection]("""{}""")
res1: cats.data.ValidatedNel[io.circe.Error,com.azavea.stac4s.StacCollection] = Invalid(NonEmptyList(DecodingFailure(Attempt to decode value on failed cursor, List(DownField(type)))))

Expected behavior
All errors are reported

Additional context
It's really hard to report useful API errors without this 😢