Add troubleshooting doc for MediaQueryData.size (#104828)

Author: bleroux

packages/flutter/lib/src/widgets/media_query.dart

@@ -159,6 +159,23 @@ class MediaQueryData {
   /// pixels are the size of the actual hardware pixels on the device. The
   /// number of physical pixels per logical pixel is described by the
   /// [devicePixelRatio].
+  ///
+  /// ## Troubleshooting
+  ///
+  /// It is considered bad practice to cache and later use the size returned
+  /// by `MediaQuery.of(context).size`. It will make the application non responsive
+  /// and might lead to unexpected behaviors.
+  /// For instance, during startup, especially in release mode, the first returned
+  /// size might be (0,0). The size will be updated when the native platform
+  /// reports the actual resolution.
+  ///
+  /// See the article on [Creating responsive and adaptive
+  /// apps](https://docs.flutter.dev/development/ui/layout/adaptive-responsive)
+  /// for an introduction.
+  ///
+  /// See also:
+  ///
+  ///  * [FlutterView.physicalSize], which returns the size in physical pixels.
   final Size size;
 
   /// The number of device pixels for each logical pixel. This number might not