Add JS method to collapse selection in both composer

Collapsing a selection means removing it and keep the cursor at the
end. It will be needed by the scribe for "Insert" action where we
want to insert a text at the cursor even if the user selected text.

lib/features/composer/presentation/widgets/web/web_editor_widget.dart

@@ -185,6 +185,10 @@ class _WebEditorState extends State<WebEditorWidget> with TextSelectionMixin {
             name: HtmlUtils.registerSelectionChangeListener.name,
             script: HtmlUtils.registerSelectionChangeListener.script,
           ),
+          WebScript(
+            name: HtmlUtils.collapseSelectionToEnd.name,
+            script: HtmlUtils.collapseSelectionToEnd.script,
+          ),
           WebScript(
             name: HtmlUtils.recalculateEditorHeight(maxHeight: maxHeight).name,
             script: HtmlUtils.recalculateEditorHeight(maxHeight: maxHeight).script,