enhance(ResolveFieldValue): add async collection language

and some baseline collection language for comparison

extracted from graphql#742

Authored-by: Rob Richard <rob@1stdibs.com>

spec/Section 6 -- Execution.md

@@ -650,6 +650,12 @@ As an example, this might accept the {objectType} `Person`, the {field}
 {"soulMate"}, and the {objectValue} representing John Lennon. It would be
 expected to yield the value representing Yoko Ono.
 
+List values are resolved similarly. For example, {ResolveFieldValue} might also
+accept the {objectType} `MusicBand`, the {field} {"members"}, and the
+{objectValue} representing the Beatles. It would be expected to yield a
+collection of values representing John Lennon, Paul McCartney, Ringo Starr and
+George Harrison.
+
 ResolveFieldValue(objectType, objectValue, fieldName, argumentValues):
 
 - Let {resolver} be the internal function provided by {objectType} for
@@ -660,7 +666,8 @@ ResolveFieldValue(objectType, objectValue, fieldName, argumentValues):
 Note: It is common for {resolver} to be asynchronous due to relying on reading
 an underlying database or networked service to produce a value. This
 necessitates the rest of a GraphQL executor to handle an asynchronous execution
-flow.
+flow. In addition, an implementation for collections may leverage asynchronous
+iterators or asynchronous generators provided by many programming languages.
 
 ### Value Completion