The previous `Reflector` implementation did not use post barriers, so we could crash when storing nursery objects in a `Reflector` structure that were later moved out of the nursery.
- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes fix#15085
- [X] There are tests for these changes
Source-Repo: https://github.com/servo/servo
Source-Revision: 023a9c55ec84413b9c097c4963f5c3e1b4885eb9