feat(ui): show custom action on context menu (#1353)

* fix(ui): Show message custom actions on desktop context menu.

* fix(ui): don't handle keyboard shortcut when callback is null.

Co-authored-by: Salvatore Giordano <[email protected]>

packages/stream_chat_flutter/lib/src/keyboard_shortcuts/keyboard_shortcut_runner.dart

@@ -35,10 +35,11 @@ class KeyboardShortcutRunner extends StatelessWidget {
     return FocusableActionDetector(
       autofocus: true,
       shortcuts: {
-        enterKeySet: EnterKeyIntent(),
-        escapeKeySet: EscapeKeyIntent(),
-        rightArrowKeySet: RightArrowKeyIntent(),
-        leftArrowKeySet: LeftArrowKeyIntent(),
+        if (onEnterKeypress != null) enterKeySet: EnterKeyIntent(),
+        if (onEscapeKeypress != null) escapeKeySet: EscapeKeyIntent(),
+        if (onRightArrowKeypress != null)
+          rightArrowKeySet: RightArrowKeyIntent(),
+        if (onLeftArrowKeypress != null) leftArrowKeySet: LeftArrowKeyIntent(),
       },
       actions: {
         EnterKeyIntent: CallbackAction(