[#8010] improvement: fix resource path enumeration to accumulate parent segments

[diydriller]

What changes were proposed in this pull request?

This PR fixes the incorrect resource path enumeration logic in the GCS token provider by ensuring that multi-level paths accumulate parent segments correctly and include both non-directory and directory variants where appropriate.
Additionally, the logic that previously concatenated strings to the parent variable using + operations has been replaced with a StringBuilder for improved efficiency, and cases where resourcePath is null are now handled safely.

Why are the changes needed?

The previous implementation did not include the non-directory path segments for intermediate levels.
Additionally, repeatedly concatenating strings using the + operator introduced unnecessary overhead, and the absence of null handling for resourcePath could result in unexpected exceptions.

Fix: #8010

Does this PR introduce any user-facing change?

No new user-facing API is introduced.

How was this patch tested?

Use the test code below

  @Test
  void testGetAllResources() {
    Map<String, List<String>> checkResults =
        ImmutableMap.<String, List<String>>builder()
            .put("a/b", Arrays.asList("a", "a/", "a/b"))
            .put("a/b/", Arrays.asList("a", "a/", "a/b"))
            .put("a/b/c", Arrays.asList("a", "a/", "a/b", "a/b/", "a/b/c"))
            .put("a/b/c/", Arrays.asList("a", "a/", "a/b", "a/b/", "a/b/c"))
            .put("a", Arrays.asList("a"))
            .put("a/", Arrays.asList("a"))
            .put("", Arrays.asList(""))
            .put("/", Arrays.asList(""))
            .build();

    checkResults.forEach(
        (key, value) -> {
          List<String> parentResources = GCSTokenProvider.getAllResources(key);
          Assertions.assertArrayEquals(value.toArray(), parentResources.toArray());
        });
  }

[justinmclean]

Thanks for this