null_safety rebuild script (#1369) (#1371)

## Pre-launch Checklist

- [x] I read the [Flutter Style Guide] _recently_, and have followed its advice.
- [x] I signed the [CLA].
- [x] I read the [Contributors Guide].
- [x] I updated/added relevant documentation (doc comments with `///`).
- [x] All existing and new tests are passing.

If you need help, consider asking for advice on the #hackers-devrel channel on [Discord].

<!-- Links -->
[Flutter Style Guide]: https://github.com/flutter/flutter/wiki/Style-guide-for-Flutter-repo
[CLA]: https://cla.developers.google.com/
[Discord]: https://github.com/flutter/flutter/wiki/Chat
[Contributors Guide]: https://github.com/flutter/samples/blob/main/CONTRIBUTING.md

platform_channels/android/app/src/debug/AndroidManifest.xml

@@ -1,6 +1,7 @@
 <manifest xmlns:android="http://schemas.android.com/apk/res/android"
     package="dev.flutter.platform_channels">
-    <!-- Flutter needs it to communicate with the running application
+    <!-- The INTERNET permission is required for development. Specifically,
+         the Flutter tool needs it to communicate with the running application
          to allow setting breakpoints, to provide hot reload, etc.
     -->
     <uses-permission android:name="android.permission.INTERNET"/>

platform_channels/android/app/src/main/res/values-night/styles.xml

@@ -3,7 +3,7 @@
     <!-- Theme applied to the Android Window while the process is starting when the OS's Dark Mode setting is on -->
     <style name="LaunchTheme" parent="@android:style/Theme.Black.NoTitleBar">
         <!-- Show a splash screen on the activity. Automatically removed when
-             Flutter draws its first frame -->
+             the Flutter engine draws its first frame -->
         <item name="android:windowBackground">@drawable/launch_background</item>
     </style>
     <!-- Theme applied to the Android Window as soon as the process has started.

platform_channels/android/app/src/main/res/values/styles.xml

@@ -3,7 +3,7 @@
     <!-- Theme applied to the Android Window while the process is starting when the OS's Dark Mode setting is off -->
     <style name="LaunchTheme" parent="@android:style/Theme.Light.NoTitleBar">
         <!-- Show a splash screen on the activity. Automatically removed when
-             Flutter draws its first frame -->
+             the Flutter engine draws its first frame -->
         <item name="android:windowBackground">@drawable/launch_background</item>
     </style>
     <!-- Theme applied to the Android Window as soon as the process has started.

platform_channels/android/app/src/profile/AndroidManifest.xml

@@ -1,6 +1,7 @@
 <manifest xmlns:android="http://schemas.android.com/apk/res/android"
     package="dev.flutter.platform_channels">
-    <!-- Flutter needs it to communicate with the running application
+    <!-- The INTERNET permission is required for development. Specifically,
+         the Flutter tool needs it to communicate with the running application
          to allow setting breakpoints, to provide hot reload, etc.
     -->
     <uses-permission android:name="android.permission.INTERNET"/>