`AnyBuilderBuild` omits leading slash and has unused typeUrl parameter

[bkeryan]

AnyBuilderBuild - unrelated but this should probably prepend a '/' the same way PackToAny does.

Originally posted by @jasonmreding in #471 (comment)

On further inspection, I realized this function and AnyBuilderBuildToBuffer have an unused typeUrl parameter, which raises more questions about this code.

AB#3226306

[jasonmreding]

On further inspection, I realized this function and AnyBuilderBuildToBuffer have an unused typeUrl parameter, which raises more questions about this code.

I'm not really sure why we decided to offer both Buffer and Any variations of the same API. The LV APIs for both variations require a string type url as input which doesn't really make sense when working from an Any which already contains a field with this information. It seems like it would have been simpler to just always deal with Any so that the type URL is always packaged with the encoded message data rather than having to supply both inputs.

AnyBuilderBuildToBuffer really shouldn't have a typeUrl input at all as it isn't needed since we are only supplying the bytes of the Any. The reason it is needed for other Buffer related APIs is because we need to be able to lookup the corresponding metadata in order to know how to pack the data. However, with the Any builder APIs, no metadata is generally required as that is effectively supplied with each call to add a field to the builder. This really seems more like a raw serialization API for a generic message class than an Any builder API.