enhance(ResolveFieldValue): add async collection language

and some baseline collection language for comparison

extracted from #742

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

spec/Section 6 -- Execution.md

@@ -644,23 +644,27 @@ must only allow usage of variables of appropriate types.
 While nearly all of GraphQL execution can be described generically, ultimately
 the internal system exposing the GraphQL interface must provide values. This is
 exposed via {ResolveFieldValue}, which produces a value for a given field on a
-type for a real value.
+type for a real value. 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.
 
-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
   determining the resolved value of a field named {fieldName}.
 - Return the result of calling {resolver}, providing {objectValue} and
-  {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.
+  {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. In addition, an implementation for collections
+  may leverage asynchronous iterators or asynchronous generators provided by
+  many programming languages.
 
 ### Value Completion