Change SharedRecordType abstract getters to return lists.

Previously these abstract getters were typed as returning
iterables. Although in principle, changing the return types to lists
constrains the implementations more, in practice it makes no
difference because the only implementations are in the CFE, analzyer,
and the mini_types shared tests, and those implementations already
return lists anyhow.

Changing the abstact getters to return lists will simplify future work
by allowing code that interacts with the base SharedRecordType class
to index into the lists rather than having to iterate through them.

Change-Id: Ia257400dbb7c89aabc468be15a939e6baa36e191
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/367500
Commit-Queue: Paul Berry <paulberry@google.com>
Reviewed-by: Chloe Stefantsova <cstefantsova@google.com>
Reviewed-by: Konstantin Shcheglov <scheglov@google.com>

pkg/_fe_analyzer_shared/lib/src/types/shared_type.dart

@@ -24,9 +24,9 @@ abstract interface class SharedNamedType<Type extends SharedType> {
 /// represent a record type.
 abstract interface class SharedRecordType<Type extends SharedType>
     implements SharedType {
-  Iterable<SharedNamedType<Type>> get namedTypes;
+  List<SharedNamedType<Type>> get namedTypes;
 
-  Iterable<Type> get positionalTypes;
+  List<Type> get positionalTypes;
 }
 
 /// Common interface for data structures used by the implementations to

pkg/analyzer/lib/src/dart/element/type.dart

@@ -1131,7 +1131,7 @@ class RecordTypeImpl extends TypeImpl implements RecordType {
   String? get name => null;
 
   @override
-  Iterable<SharedNamedType<DartType>> get namedTypes => namedFields;
+  List<SharedNamedType<DartType>> get namedTypes => namedFields;
 
   @override
   bool operator ==(Object other) {

pkg/kernel/lib/ast.dart

@@ -12871,7 +12871,7 @@ class RecordType extends DartType implements SharedRecordType<DartType> {
             "in a RecordType: ${named}");
 
   @override
-  Iterable<SharedNamedType<DartType>> get namedTypes => named;
+  List<SharedNamedType<DartType>> get namedTypes => named;
 
   @override
   Nullability get nullability => declaredNullability;
@@ -12888,7 +12888,7 @@ class RecordType extends DartType implements SharedRecordType<DartType> {
       };
 
   @override
-  Iterable<DartType> get positionalTypes => positional;
+  List<DartType> get positionalTypes => positional;
 
   @override
   R accept<R>(DartTypeVisitor<R> v) {