Clarify platform support of QuillEditorConfig.onKeyPressed (#2542)

* Correct info about platform support of QuillEditorConfig.onKeyPressed

The documentation stated that this callback is only supported by desktop devices. I found that it is also supported by mobile devices when they have a hardware keyboard connected, which is great, because I needed to customize some Quill editor behavior for exactly this scenario.

* Update editor_config.dart

Fixed typo

Author: jaanus

lib/src/editor/config/editor_config.dart

@@ -139,7 +139,9 @@ class QuillEditorConfig {
 
   /// A handler for keys that are pressed when the editor is focused.
   ///
-  /// This feature is supported on **desktop devices only**.
+  /// This feature is supported on **desktop devices** and **mobile devices with a
+  /// hardware keyboard connected.** It is not supported by virtual on-screen
+  /// keyboards of touch devices.
   ///
   /// # Example:
   /// To prevent the user from removing any **Embed Object**, try: