Normalize [Entrypoint.packageFiles] paths for Windows.

sdk/lib/_internal/pub/lib/src/entrypoint.dart

Index: sdk/lib/_internal/pub/lib/src/entrypoint.dart
diff --git a/sdk/lib/_internal/pub/lib/src/entrypoint.dart b/sdk/lib/_internal/pub/lib/src/entrypoint.dart
index 86327531fc5acb6b4d67c1685718066bd4d58247..aefd115811d8c0232433c791519d379461b2e990 100644
--- a/sdk/lib/_internal/pub/lib/src/entrypoint.dart
+++ b/sdk/lib/_internal/pub/lib/src/entrypoint.dart
@@ -243,7 +243,7 @@ class Entrypoint {
             workingDir: root.dir).then((files) {
           // Git always prints files relative to the project root, but we want
           // them relative to the working directory.
-          return files.map((file) => path.join(root.dir, file));
+          return files.map((file) => path.normalize(path.join(root.dir, file)));
         });
       }