Expose NavigationRail properties to NavbarDecoration

Pre-launch Checklist

[X] I read the Contributor Guide and followed the process outlined there for submitting PRs.
[X] I listed at least one issue that this PR fixes in the description above.
[X] I updated/added relevant documentation (doc comments with ///).
[X] I added new tests to check the change I am making, or this PR is [test-exempt].
[X] All existing and new tests are passing using flutter test

If you need help, consider pinging the maintainer @maheshmnj