fix: resolve local package paths relative to the repository root (#881)

- Update `resources_example` moving the `Package.swift` under a
sub-directory.
- Resolve local Swift packages using the repository root directory.

Closes #869.

Author: cgrindel

examples/resources_example/BUILD.bazel

@@ -32,5 +32,6 @@ swift_update_packages(
     name = "swift_update_pkgs",
     gazelle = ":gazelle_bin",
     generate_swift_deps_for_workspace = False,
+    package_manifest = "swift/Package.swift",
     update_bzlmod_stanzas = True,
 )