fix(amino/json): use AminoMarshaler reprType info

When checking if `info.IsJSONAnyValueType`, if this type is a
AminoMarshaler, then also check `info.ReprType.IsJSONAnyValueType`.

This prevents a panics that happens during the sanity check phase of
`encodeReflectJSONInterface()` when the type `ConcreteInfo` doesn't match
the JSON structure. For instance, before that fix, that used to happen
with `BigintValue` which is a struct (so expected JSON is `{...}` and
`IsJSONAnyValueType=false`), but is marshaled into a simple string (so
expected JSON is only `"..."`, and `ReprType.IsJSONAnyValueType=true`).