asyncIterable: locate async iterator errors to the collection (graphql#3899)

Currently, they are presented as errors in the next pending item.

Of course, there may or not be a next pending item; there may not be a
way to definitively know the reason for the error, such that the error
is a function of a problem with the collection itself.

As discussed in a prior incremental delivery WG meeting, this must be
changed for both the non-streaming and streaming cases; this PR makes
the minor adjustments addressing both cases.

Author: yaacovCR

src/execution/__tests__/lists-test.ts

@@ -141,12 +141,12 @@ describe('Execute: Accepts async iterables as list value', () => {
     }
 
     expectJSON(await complete({ listField })).toDeepEqual({
-      data: { listField: ['two', '4', null] },
+      data: { listField: null },
       errors: [
         {
           message: 'bad',
           locations: [{ line: 1, column: 3 }],
-          path: ['listField', 2],
+          path: ['listField'],
         },
       ],
     });

src/execution/execute.ts

@@ -779,9 +779,7 @@ async function completeAsyncIteratorValue(
         break;
       }
     } catch (rawError) {
-      handleFieldError(rawError, exeContext, itemType, fieldGroup, itemPath);
-      completedResults.push(null);
-      break;
+      throw locatedError(rawError, fieldGroup, pathToArray(path));
     }
 
     if (