Make Linux shell plugin constructor descriptions consistent (#18940)

shell/platform/linux/fl_key_event_plugin.h

@@ -28,7 +28,8 @@ G_DECLARE_FINAL_TYPE(FlKeyEventPlugin,
  * fl_key_event_plugin_new:
  * @messenger: an #FlBinaryMessenger.
  *
- * Creates a #FlKeyEventPlugin.
+ * Creates a new plugin that implements SystemChannels.keyEvent from the
+ * Flutter services library.
  *
  * Returns: a new #FlKeyEventPlugin.
  */

shell/platform/linux/fl_text_input_plugin.h

@@ -20,7 +20,7 @@ G_DECLARE_FINAL_TYPE(FlTextInputPlugin,
 /**
  * FlTextInputPlugin:
  *
- * #FlTextInputPlugin is a text_input channel that implements the shell side
+ * #FlTextInputPlugin is a plugin that implements the shell side
  * of SystemChannels.textInput from the Flutter services library.
  */