Fixes #138773, port autocomplete to OverlayPortal (#140285)

Fixes #138773, port autocomplete to OverlayPortal

packages/flutter/lib/src/material/autocomplete.dart

@@ -126,6 +126,7 @@ class Autocomplete<T extends Object> extends StatelessWidget {
           displayStringForOption: displayStringForOption,
           onSelected: onSelected,
           options: options,
+          openDirection: optionsViewOpenDirection,
           maxOptionsHeight: optionsMaxHeight,
         );
       },
@@ -166,6 +167,7 @@ class _AutocompleteOptions<T extends Object> extends StatelessWidget {
     super.key,
     required this.displayStringForOption,
     required this.onSelected,
+    required this.openDirection,
     required this.options,
     required this.maxOptionsHeight,
   });
@@ -173,14 +175,19 @@ class _AutocompleteOptions<T extends Object> extends StatelessWidget {
   final AutocompleteOptionToString<T> displayStringForOption;
 
   final AutocompleteOnSelected<T> onSelected;
+  final OptionsViewOpenDirection openDirection;
 
   final Iterable<T> options;
   final double maxOptionsHeight;
 
   @override
   Widget build(BuildContext context) {
+    final AlignmentDirectional optionsAlignment = switch (openDirection) {
+      OptionsViewOpenDirection.up => AlignmentDirectional.bottomStart,
+      OptionsViewOpenDirection.down => AlignmentDirectional.topStart,
+    };
     return Align(
-      alignment: Alignment.topLeft,
+      alignment: optionsAlignment,
       child: Material(
         elevation: 4.0,
         child: ConstrainedBox(

packages/flutter/test/material/autocomplete_test.dart

@@ -552,9 +552,11 @@ void main() {
       await tester.pumpWidget(
         MaterialApp(
           home: Scaffold(
-            body: Autocomplete<String>(
-              optionsViewOpenDirection: OptionsViewOpenDirection.up,
-              optionsBuilder: (TextEditingValue textEditingValue) => <String>['a'],
+            body: Center(
+              child: Autocomplete<String>(
+                optionsViewOpenDirection: OptionsViewOpenDirection.up,
+                optionsBuilder: (TextEditingValue textEditingValue) => <String>['aa'],
+              ),
             ),
           ),
         ),
@@ -562,6 +564,10 @@ void main() {
       final OptionsViewOpenDirection actual = tester.widget<RawAutocomplete<String>>(find.byType(RawAutocomplete<String>))
         .optionsViewOpenDirection;
       expect(actual, equals(OptionsViewOpenDirection.up));
+
+      await tester.tap(find.byType(RawAutocomplete<String>));
+      await tester.enterText(find.byType(RawAutocomplete<String>), 'a');
+      expect(find.text('aa').hitTestable(), findsOneWidget);
     });
   });
 }