Replace platform check with swtich (#24752)

Generally, we should always use default-less switches for
platform-specific behaviour so we're forced to make a conscious decision
on each instance of such behaviour any time we add support for a new
platform.

packages/flutter/lib/src/material/scaffold.dart

@@ -1777,7 +1777,8 @@ class ScaffoldState extends State<Scaffold> with TickerProviderStateMixin {
       removeBottomPadding: true,
     );
 
-    if (themeData.platform == TargetPlatform.iOS) {
+    switch (themeData.platform) {
+      case TargetPlatform.iOS:
         _addIfNonNull(
           children,
           GestureDetector(
@@ -1792,6 +1793,10 @@ class ScaffoldState extends State<Scaffold> with TickerProviderStateMixin {
           removeRightPadding: false,
           removeBottomPadding: true,
         );
+        break;
+      case TargetPlatform.android:
+      case TargetPlatform.fuchsia:
+        break;
     }
 
     if (_endDrawerOpened) {