Resolve fragments before execution #541
Description
Currently, fragments are resolved during execution, which e.g. makes parts of the implementation during execution a bit more verbose than necessary. Also, looking at Field Collection the spec seems to suggest it should be done (emphasis by me):
Before execution, each selection set is converted to a collected fields map by collecting all fields with the same response name, including those in referenced fragments, into an individual field set
Might also resolve #406