Fix spelling error and clarify universal flag (#36331)

packages/flutter_tools/lib/src/cache.dart

@@ -26,7 +26,7 @@ class DevelopmentArtifact {
   /// This should match the flag name in precache.dart
   final String name;
 
-  /// Whether this artifact should not be usable on stable branches.
+  /// Whether this artifact should be unavailable on stable branches.
   final bool unstable;
 
   /// Artifacts required for Android development.
@@ -35,7 +35,7 @@ class DevelopmentArtifact {
   /// Artifacts required for iOS development.
   static const DevelopmentArtifact iOS = DevelopmentArtifact._('ios');
 
-  /// Artifacts required for web development,
+  /// Artifacts required for web development.
   static const DevelopmentArtifact web = DevelopmentArtifact._('web', unstable: true);
 
   /// Artifacts required for desktop macOS.
@@ -44,13 +44,13 @@ class DevelopmentArtifact {
   /// Artifacts required for desktop Windows.
   static const DevelopmentArtifact windows = DevelopmentArtifact._('windows', unstable: true);
 
-  /// Artifacts required for desktop linux.
+  /// Artifacts required for desktop Linux.
   static const DevelopmentArtifact linux = DevelopmentArtifact._('linux', unstable: true);
 
   /// Artifacts required for Fuchsia.
   static const DevelopmentArtifact fuchsia = DevelopmentArtifact._('fuchsia', unstable: true);
 
-  /// Artifacts required by all developments.
+  /// Artifacts required for any development platform.
   static const DevelopmentArtifact universal = DevelopmentArtifact._('universal');
 
   /// The values of DevelopmentArtifacts.

packages/flutter_tools/lib/src/commands/precache.dart

@@ -16,21 +16,21 @@ class PrecacheCommand extends FlutterCommand {
     argParser.addFlag('force', abbr: 'f', negatable: false,
         help: 'Force downloading of artifacts.');
     argParser.addFlag('android', negatable: true, defaultsTo: true,
-        help: 'Precache artifacts for Android development');
+        help: 'Precache artifacts for Android development.');
     argParser.addFlag('ios', negatable: true, defaultsTo: true,
-        help: 'Precache artifacts for iOS developemnt');
+        help: 'Precache artifacts for iOS development.');
     argParser.addFlag('web', negatable: true, defaultsTo: false,
-        help: 'Precache artifacts for web development');
+        help: 'Precache artifacts for web development.');
     argParser.addFlag('linux', negatable: true, defaultsTo: false,
-        help: 'Precache artifacts for linux desktop development');
+        help: 'Precache artifacts for Linux desktop development.');
     argParser.addFlag('windows', negatable: true, defaultsTo: false,
-        help: 'Precache artifacts for windows desktop development');
+        help: 'Precache artifacts for Windows desktop development.');
     argParser.addFlag('macos', negatable: true, defaultsTo: false,
-        help: 'Precache artifacts for macOS desktop development');
+        help: 'Precache artifacts for macOS desktop development.');
     argParser.addFlag('fuchsia', negatable: true, defaultsTo: false,
-        help: 'Precache artifacts for Fuchsia development');
+        help: 'Precache artifacts for Fuchsia development.');
     argParser.addFlag('universal', negatable: true, defaultsTo: true,
-        help: 'Precache artifacts required for all developments');
+        help: 'Precache artifacts required for any development platform.');
   }
 
   @override