Mixin `TextInputClient` to include `insertContent` implementation (#1618)

simplistic_editor/lib/basic_text_input_client.dart

@@ -40,8 +40,7 @@ class BasicTextInputClient extends StatefulWidget {
 }
 
 class BasicTextInputClientState extends State<BasicTextInputClient>
-    with TextSelectionDelegate
-    implements DeltaTextInputClient {
+    with TextSelectionDelegate, TextInputClient, DeltaTextInputClient {
   final GlobalKey _textKey = GlobalKey();
   late AppStateWidgetState manager;
   final ClipboardStatusNotifier? _clipboardStatus =

tool/flutter_ci_script_master.sh

@@ -50,8 +50,7 @@ declare -ar PROJECT_NAMES=(
     "provider_counter"
     "provider_shopper"
     "simplistic_calculator"
-    # TODO(DomesticMouse): https://github.com/flutter/samples/issues/1616
-    # "simplistic_editor"
+    "simplistic_editor"
     "testing_app"
     "veggieseasons"
     "web/_tool"