[flutter_tools] Fix local engine preview device (flutter#138046)

Fixes flutter#137982

Author: christopherfujino

packages/flutter_tools/lib/src/artifacts.dart

@@ -1028,7 +1028,12 @@ class CachedLocalEngineArtifacts implements Artifacts {
       case Artifact.flutterToolsFileGenerators:
         return _getFileGeneratorsPath();
       case Artifact.flutterPreviewDevice:
-        throw UnimplementedError('The preview device is not supported with local engine builds');
+        return _backupCache.getArtifactPath(
+          artifact,
+          platform: platform,
+          mode: mode,
+          environmentType: environmentType,
+        );
     }
   }
 

packages/flutter_tools/test/general.shard/artifacts_test.dart

@@ -329,6 +329,14 @@ void main() {
           'snapshots', 'frontend_server_aot.dart.snapshot')
       );
 
+      expect(
+        artifacts.getArtifactPath(
+          Artifact.flutterPreviewDevice,
+          platform: TargetPlatform.windows_x64,
+        ),
+        fileSystem.path.join('root', 'bin', 'cache', 'artifacts',
+          'flutter_preview', 'flutter_preview.exe'),
+      );
 
       fileSystem.file(fileSystem.path.join('/out', 'host_debug_unopt', 'impellerc'))
         .createSync(recursive: true);