Performing sub-doc SetDoc on the entire document should still use the transcoder

Currently, all multi-lookup operations pass through the transcoder to deserialize. However, multi-mutate operations skip the transcoder and go directly to the serializer. This is fine for JSON content, but means that content such as a byte array meant to be written raw is serialized by the JSON serializer. It will then fail to read when performing a multi-lookup "GetFull" operation because that does pass through the transcoder's Decode<T> method.

When working with true sub-document operations, this is probably fine. You are clearly working with JSON if you're setting a property on a JSON document. However, sub-doc operations are also used for getting/settings XATTRs. This bug means that there is no way to set a byte-array document with XATTRs as a single operation, it would require one traditional SET operation followed by a separate operation to set the XATTRs.

Additionally, the handling is also inconsistent on nested properties. In this case, the multi-mutate operation is correctly assuming that everything should be serialized as JSON, but the multi-lookup is out of sync because it always uses the Transcoder not just the JSON serializer.

Repro:

var transcoder = new LegacyTranscoder(new DefaultSerializer());

var mutateInSpecs = new List<MutateInSpec>(2)

{

    MutateInSpec.SetDoc(new byte[] { 1, 2, 3, 4 });

    MutateInSpec.Upsert("test_attr", "foo", isXattr: true);

};

var mutateInOptions = new MutateInOptions()

    .Transcoder(transcoder)

    .StoreSemantics(StoreSemantics.Upsert);

await collection.MutateInAsync("key", mutateInSpecs , mutateInOptions);

var lookupInSpecs = new List<LookupInSpecs>(2)

{

    builder.GetFull();

    LookupInSpec.Get("test_attr", isXattr: true);

};

var lookupInOptions = new LookupInOptions()

    .Transcoder(transcoder);

var result = await collection.LookupInAsync("key", lookupInSpecs, lookupInOptions);

// Fails with an exception because the JSON serializer encoded as a Base64 string,

// but we're decoding as a byte array currently

var bytes = result.ContentAs<byte[]>(0);

// Fails because "foo" was serialized as a JSON string, with wrapping quotes, but 

// the deserializer is passing through the LegacyTranscoder which expects raw strings

// It seems like gets with a path shouldn't pass through the transcoder.

Assert.Equal("foo", result.ContentAs<string>(1));