[flutter_plugin_tools] Validate pubspec description (#4396)

pub.dev deducts points for having a pubspec.yaml `description` that is too short or too long; several of our plugins are losing points on this. To ensure that we are following—and modeling—best practices, this adds a check that our `description` fields meet pub.dev expectations.

Fixes our existing violations. Two are not published even though this only takes effect once published:
- camera: We change this plugin pretty frequently, so this should go out soon without adding a release just for this trivial issue.
- wifi_info_flutter: This is deprecated, so we don't plan to release it. It has to be fixed to allow the tool change to land though.

script/tool/lib/src/pubspec_check_command.dart

@@ -126,6 +126,18 @@ class PubspecCheckCommand extends PackageLoopingCommand {
             '${indentation * 2}$_expectedIssueLinkFormat<package label>');
         passing = false;
       }
+
+      // Don't check descriptions for federated package components other than
+      // the app-facing package, since they are unlisted, and are expected to
+      // have short descriptions.
+      if (!package.isPlatformInterface && !package.isPlatformImplementation) {
+        final String? descriptionError =
+            _checkDescription(pubspec, package: package);
+        if (descriptionError != null) {
+          printError('$indentation$descriptionError');
+          passing = false;
+        }
+      }
     }
 
     return passing;
@@ -180,6 +192,27 @@ class PubspecCheckCommand extends PackageLoopingCommand {
     return errorMessages;
   }
 
+  // Validates the "description" field for a package, returning an error
+  // string if there are any issues.
+  String? _checkDescription(
+    Pubspec pubspec, {
+    required RepositoryPackage package,
+  }) {
+    final String? description = pubspec.description;
+    if (description == null) {
+      return 'Missing "description"';
+    }
+
+    if (description.length < 60) {
+      return '"description" is too short. pub.dev recommends package '
+          'descriptions of 60-180 characters.';
+    }
+    if (description.length > 180) {
+      return '"description" is too long. pub.dev recommends package '
+          'descriptions of 60-180 characters.';
+    }
+  }
+
   bool _checkIssueLink(Pubspec pubspec) {
     return pubspec.issueTracker
             ?.toString()