Improve jax.Array documentation

[hawkinsp]

https://jax.readthedocs.io/en/latest/_autosummary/jax.Array.html#jax.Array

Many of the methods and properties of jax.Array are not sufficiently documented.

• I don't think ArrayImpl appears in the documentation at all. It at least needs an explanation.

• For pretty much all methods, especially those that don't correspond to NumPy APIs, we should link to documentation that shows an example of usage, including a typical input and output.

• Some of the documentation is very cryptic and needs more details. For example:

addressable_data(index) | Return an array of the addressable data at a particular index.

I'm none the wiser from that description what exactly index is. Is it an integer? Is it a NumPy index? If it is an integer, what does the integer mean? What is the "index-th addressable data"?

addressable_shards | List of addressable shards.

What type of object is a shard? Does they come in any particular order?

• Some attributes aren't documented as best I can tell, e.g., device and devices.

[jakevdp]

I don't think ArrayImpl appears in the documentation at all

This came up when we were creating the linked page. I recall @yashk2810 was a strong -1 on documenting ArrayImpl. Some impl-only functions are not documented, becuase they don't exist on the base Array class.

For the others, getting more detailed docs is mainly about changing how we declare jax.Array in the sphinx sources.

[hawkinsp]

I think we should document the existence of ArrayImpl but not say a whole lot about it, pointing the user to `Array.