new_dm_sheet: Make searching insensitive to diacritics

We didn't have an issue for this, but I guess it would've been
quietly fixed in a future where we've switched the filtering/sorting
fully over to our autocomplete machinery, which we have a TODO for.

Author: chrisbobbe

lib/widgets/new_dm_sheet.dart

@@ -87,12 +87,14 @@ class _NewDmPickerState extends State<NewDmPicker> with PerAccountStoreAwareStat
   void _updateFilteredUsers(PerAccountStore store) {
     final excludeSelfUser = selectedUserIds.isNotEmpty
       && !selectedUserIds.contains(store.selfUserId);
-    final searchTextLower = searchController.text.toLowerCase();
+    final normalizedQuery =
+      AutocompleteQuery.lowercaseAndStripDiacritics(searchController.text);
 
     final result = <User>[];
     for (final user in sortedUsers) {
       if (excludeSelfUser && user.userId == store.selfUserId) continue;
-      if (user.fullName.toLowerCase().contains(searchTextLower)) {
+      final normalizedName = AutocompleteQuery.lowercaseAndStripDiacritics(user.fullName);
+      if (normalizedName.contains(normalizedQuery)) {
         result.add(user);
       }
     }

test/widgets/new_dm_sheet_test.dart

@@ -175,13 +175,14 @@ void main() {
       check(findText(includePlaceholders: false, 'Muted user')).findsNothing();
       check(findText(includePlaceholders: false, 'Alice Anderson')).findsOne();
       check(findText(includePlaceholders: false, 'Charlie Carter')).findsOne();
-      check(find.byIcon(ZulipIcons.check_circle_unchecked)).findsExactly(2);
+      check(findText(includePlaceholders: false, 'Édith Piaf')).findsOne();
+      check(find.byIcon(ZulipIcons.check_circle_unchecked)).findsExactly(3);
     });
 
     // TODO test sorting by recent-DMs
     // TODO test that scroll position resets on query change
 
-    testWidgets('search is case-insensitive', (tester) async {
+    testWidgets('search is case- and diacritics-insensitive', (tester) async {
       await setupSheet(tester, users: testUsers);
       await tester.enterText(find.byType(TextField), 'alice');
       await tester.pump();
@@ -190,6 +191,14 @@ void main() {
       await tester.enterText(find.byType(TextField), 'ALICE');
       await tester.pump();
       check(findText(includePlaceholders: false, 'Alice Anderson')).findsOne();
+
+      await tester.enterText(find.byType(TextField), 'alicé');
+      await tester.pump();
+      check(findText(includePlaceholders: false, 'Alice Anderson')).findsOne();
+
+      await tester.enterText(find.byType(TextField), 'edith');
+      await tester.pump();
+      check(findText(includePlaceholders: false, 'Édith Piaf')).findsOne();
     });
 
     testWidgets('partial name and last name search handling', (tester) async {