de-duplicate mocked package:meta

(We should do the same for `package:flutter` but that will likely require some updates to the version stored in server.)


Change-Id: I262886a3522e19f86a7ba4ae46a50c48090c8d95
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/324880
Reviewed-by: Brian Wilkerson <[email protected]>
Commit-Queue: Phil Quitslund <[email protected]>

Author: pq

pkg/linter/test_data/mock_packages/meta/lib/meta.dart

@@ -15,7 +15,7 @@
     },
     {
       "name": "meta",
-      "rootUri": "../../mock_packages/meta/",
+      "rootUri": "../../../../analysis_server/test/mock_packages/meta/",
       "packageUri": "lib/",
       "languageVersion": "2.17"
     }

pkg/linter/test_data/mock_packages/meta/pubspec.yaml

@@ -0,0 +1,2 @@
+# Required for mock packages.
+!.dart_tool