Improve doctor output on incomplete Visual Studio installation (#133390)

Flutter doctor warns if the user is updating Visual Studio or has paused
a Visual Studio update. The current output recommends reinstalling
Visual Studio. This is unnecessary as the user should be able to use the
Visual Studio Installer app to complete the installation:


![image](https://github.com/flutter/flutter/assets/737941/49547413-ece1-4214-a971-f512bc39419f)

This message is covered by this existing test:


https://github.com/flutter/flutter/blob/229b74d987720a0437039b6e44e13f20fb94ad51/packages/flutter_tools/test/general.shard/windows/visual_studio_validator_test.dart#L68-L81

## Pre-launch Checklist

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there for submitting PRs.
- [x] I read the [Tree Hygiene] wiki page, which explains my
responsibilities.
- [x] I read and followed the [Flutter Style Guide], including [Features
we expect every widget to implement].
- [x] I signed the [CLA].
- [x] I listed at least one issue that this PR fixes in the description
above.
- [x] I updated/added relevant documentation (doc comments with `///`).
- [x] I added new tests to check the change I am making, or this PR is
[test-exempt].
- [x] All existing and new tests are passing.

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

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packages/flutter_tools/lib/src/base/user_messages.dart

@@ -239,7 +239,8 @@ class UserMessages {
       'supported by Flutter yet.';
   String get visualStudioNotLaunchable =>
       'The current Visual Studio installation is not launchable. Please reinstall Visual Studio.';
-  String get visualStudioIsIncomplete => 'The current Visual Studio installation is incomplete. Please reinstall Visual Studio.';
+  String get visualStudioIsIncomplete => 'The current Visual Studio installation is incomplete.\n'
+      'Please use Visual Studio Installer to complete the installation or reinstall Visual Studio.';
   String get visualStudioRebootRequired => 'Visual Studio requires a reboot of your system to complete installation.';
 
   // Messages used in LinuxDoctorValidator

packages/flutter_tools/test/general.shard/windows/visual_studio_validator_test.dart

@@ -60,9 +60,12 @@ void main() {
       fakeVisualStudio.isPrerelease = true;
 
       final ValidationResult result = await validator.validate();
-      final ValidationMessage expectedMessage = ValidationMessage(userMessages.visualStudioIsPrerelease);
+      const ValidationMessage expectedMessage = ValidationMessage(
+        'The current Visual Studio installation is a pre-release version. '
+        'It may not be supported by Flutter yet.',
+      );
 
-      expect(result.messages.contains(expectedMessage), true);
+      expect(result.messages, contains(expectedMessage));
     });
 
     testWithoutContext('Emits a partial status when Visual Studio installation is incomplete', () async {
@@ -74,9 +77,12 @@ void main() {
       fakeVisualStudio.isComplete = false;
 
       final ValidationResult result = await validator.validate();
-      final ValidationMessage expectedMessage = ValidationMessage.error(userMessages.visualStudioIsIncomplete);
+      const ValidationMessage expectedMessage = ValidationMessage.error(
+        'The current Visual Studio installation is incomplete.\n'
+        'Please use Visual Studio Installer to complete the installation or reinstall Visual Studio.',
+      );
 
-      expect(result.messages.contains(expectedMessage), true);
+      expect(result.messages, contains(expectedMessage));
       expect(result.type, ValidationType.partial);
     });
 
@@ -89,9 +95,11 @@ void main() {
       fakeVisualStudio.isRebootRequired = true;
 
       final ValidationResult result = await validator.validate();
-      final ValidationMessage expectedMessage = ValidationMessage.error(userMessages.visualStudioRebootRequired);
+      const ValidationMessage expectedMessage = ValidationMessage.error(
+        'Visual Studio requires a reboot of your system to complete installation.',
+      );
 
-      expect(result.messages.contains(expectedMessage), true);
+      expect(result.messages, contains(expectedMessage));
       expect(result.type, ValidationType.partial);
     });
 
@@ -104,9 +112,11 @@ void main() {
       fakeVisualStudio.isLaunchable = false;
 
       final ValidationResult result = await validator.validate();
-      final ValidationMessage expectedMessage = ValidationMessage.error(userMessages.visualStudioNotLaunchable);
+      const ValidationMessage expectedMessage = ValidationMessage.error(
+        'The current Visual Studio installation is not launchable. Please reinstall Visual Studio.',
+      );
 
-      expect(result.messages.contains(expectedMessage), true);
+      expect(result.messages, contains(expectedMessage));
       expect(result.type, ValidationType.partial);
     });
 
@@ -118,14 +128,13 @@ void main() {
       configureMockVisualStudioAsTooOld();
 
       final ValidationResult result = await validator.validate();
-      final ValidationMessage expectedMessage = ValidationMessage.error(
-        userMessages.visualStudioTooOld(
-          fakeVisualStudio.minimumVersionDescription,
-          fakeVisualStudio.workloadDescription,
-        ),
+      const ValidationMessage expectedMessage = ValidationMessage.error(
+        'Visual Studio 2019 or later is required.\n'
+        'Download at https://visualstudio.microsoft.com/downloads/.\n'
+        'Please install the "Desktop development" workload, including all of its default components',
       );
 
-      expect(result.messages.contains(expectedMessage), true);
+      expect(result.messages, contains(expectedMessage));
       expect(result.type, ValidationType.partial);
     });
 
@@ -161,10 +170,11 @@ void main() {
       configureMockVisualStudioAsInstalled();
 
       final ValidationResult result = await validator.validate();
-      final ValidationMessage expectedDisplayNameMessage = ValidationMessage(
-        userMessages.visualStudioVersion(fakeVisualStudio.displayName!, fakeVisualStudio.fullVersion!));
+      const ValidationMessage expectedDisplayNameMessage = ValidationMessage(
+        'Visual Studio Community 2019 version 16.2',
+      );
 
-      expect(result.messages.contains(expectedDisplayNameMessage), true);
+      expect(result.messages, contains(expectedDisplayNameMessage));
       expect(result.type, ValidationType.success);
     });
 
@@ -176,13 +186,13 @@ void main() {
       configureMockVisualStudioAsNotInstalled();
 
       final ValidationResult result = await validator.validate();
-      final ValidationMessage expectedMessage = ValidationMessage.error(
-        userMessages.visualStudioMissing(
-          fakeVisualStudio.workloadDescription,
-        ),
+      const ValidationMessage expectedMessage = ValidationMessage.error(
+        'Visual Studio not installed; this is necessary to develop Windows apps.\n'
+        'Download at https://visualstudio.microsoft.com/downloads/.\n'
+        'Please install the "Desktop development" workload, including all of its default components'
       );
 
-      expect(result.messages.contains(expectedMessage), true);
+      expect(result.messages, contains(expectedMessage));
       expect(result.type, ValidationType.missing);
     });
   });