Enable credential autofill for signup and login (#56)

frontend/app/test/two_factor_test.dart

@@ -148,13 +148,38 @@ void main() {
     await signIn(t);
     expect(find.byKey(const ValueKey('two-factor-code')), findsOneWidget);
     expect(find.byKey(const ValueKey('preview-result')), findsNothing);
+    expect(
+      t.testTextInput.log,
+      isNot(
+        contains(
+          isMethodCall('TextInput.finishAutofillContext', arguments: true),
+        ),
+      ),
+    );
     expect(
       analytics.events.where((e) => e.kind == JourneyKind.login && e.terminal),
       isEmpty,
     );
+    await t.enterText(find.byKey(const ValueKey('two-factor-code')), '000000');
+    await tapFactor(t, 'two-factor-confirm');
+    expect(find.byKey(const ValueKey('two-factor-error')), findsOneWidget);
+    expect(
+      t.testTextInput.log,
+      isNot(
+        contains(
+          isMethodCall('TextInput.finishAutofillContext', arguments: true),
+        ),
+      ),
+    );
     await t.enterText(find.byKey(const ValueKey('two-factor-code')), '123456');
     await tapFactor(t, 'two-factor-confirm');
     expect(find.byKey(const ValueKey('account-eur')), findsOneWidget);
+    expect(
+      t.testTextInput.log,
+      contains(
+        isMethodCall('TextInput.finishAutofillContext', arguments: true),
+      ),
+    );
     final login = analytics.events
         .where((e) => e.kind == JourneyKind.login)
         .toList();
@@ -172,6 +197,20 @@ void main() {
     await signIn(t);
     await tapFactor(t, 'two-factor-cancel');
     expect(find.byKey(const ValueKey('email')), findsOneWidget);
+    expect(
+      t.testTextInput.log,
+      contains(
+        isMethodCall('TextInput.finishAutofillContext', arguments: false),
+      ),
+    );
+    expect(
+      t.testTextInput.log,
+      isNot(
+        contains(
+          isMethodCall('TextInput.finishAutofillContext', arguments: true),
+        ),
+      ),
+    );
     expect(find.byKey(const ValueKey('preview-result')), findsNothing);
     expect(
       t