Uniqueness of field aliases

[wutsch0]

Both the latest released spec and the working draft don't contain any information on field alias uniqueness requirements. Field aliases need to be unique at least within the same object by common sense, but it is not specified if they need to be unique globally within the whole request or can be reused in different objects.

Deciding for the one or the other could be a breaking change for existing implementations.

To my understanding of the Contribution guidelines, deciding on that topic requires to follow the RFC process, which requires a champion to pick up this topic :pray: