resolve issues #108 and duplicate #105 (#109)

* resolve issues #986, duplicate #1021, maybe others. TextInputClient added breaking change requiring three new overrides. empty implementation provided here to stop errors. See https://docs.flutter.dev/release/breaking-changes/scribble-text-input-client

* WidgetsBinding.instance is non-nullable in flutter 3

lib/src/chips_input.dart

@@ -133,7 +133,7 @@ class ChipsInputState<T> extends State<ChipsInput<T>>
     _focusNode.addListener(_handleFocusChanged);
     _nodeAttachment = _focusNode.attach(context);
 
-    WidgetsBinding.instance?.addPostFrameCallback((_) async {
+    WidgetsBinding.instance.addPostFrameCallback((_) async {
       _initOverlayEntry();
       if (mounted && widget.autofocus) {
         FocusScope.of(context).autofocus(_focusNode);
@@ -292,7 +292,7 @@ class ChipsInputState<T> extends State<ChipsInput<T>>
 
   void _scrollToVisible() {
     Future.delayed(const Duration(milliseconds: 300), () {
-      WidgetsBinding.instance?.addPostFrameCallback((_) async {
+      WidgetsBinding.instance.addPostFrameCallback((_) async {
         final renderBox = context.findRenderObject() as RenderBox;
         await Scrollable.of(context)?.position.ensureVisible(renderBox);
       });
@@ -451,7 +451,7 @@ class ChipsInputState<T> extends State<ChipsInput<T>>
 
     return NotificationListener<SizeChangedLayoutNotification>(
       onNotification: (SizeChangedLayoutNotification val) {
-        WidgetsBinding.instance?.addPostFrameCallback((_) async {
+        WidgetsBinding.instance.addPostFrameCallback((_) async {
           _suggestionsBoxController.overlayEntry?.markNeedsBuild();
         });
         return true;
@@ -485,4 +485,13 @@ class ChipsInputState<T> extends State<ChipsInput<T>>
       ),
     );
   }
+
+  @override
+  void showToolbar() {}
+
+  @override
+  void insertTextPlaceholder(Size size) {}
+
+  @override
+  void removeTextPlaceholder() {}
 }