Deprecate `jax.clear_backends`.
`jax.clear_backends` does not necessarily do what its name suggests and can lead to unexpected consequences, e.g., it will not destroy existing backends and release corresponding owned resources. Use `jax.clear_caches` if you only want to clean up compilation caches. For backward compatibilty or you really need to switch/reinitialize the default backend, use `jax.extend.backend.clear_backends`.
PiperOrigin-RevId: 616946337
