Limit jax._src.lib to shims around jaxlib and nothing else.
The goal of this change is to avoid a dependency cycle between the rest of jax and jax._src.lib in a Bazel build. This allows the types for jax._src.lib to be inferred by pytype in isolation without referring to the rest of JAX.
PiperOrigin-RevId: 512922397
Currently
```
import jax
```
populates `jax._src` in the names exported from JAX. This change prepares for not exporting `jax._src` by default.
In particular, explicitly import modules from jax._src and refer to those imports rather than assuming jax._src contents will be around later. This is a common pattern in tests.
This change does not yet remove any exported names.
Issue https://github.com/google/jax/issues/11951
PiperOrigin-RevId: 469480816
