Expose lookupTables through public API

[marcysutton]

As part of our ongoing Support agreement, we had a request to expose the ARIA lookupTables through the public axe-core API. These are pretty stable, so I don't anticipate much work in the way of maintaining backwards compatibility.

I believe the goal is to expose the roles, attributes, and global attributes inside of rules and checks.

https://github.com/dequelabs/axe-core/blob/develop/lib/commons/aria/index.js

[marcysutton]

These are available through the global axe object:

axe.commons.aria._lut

Should we alias this when we document it?

[WilcoFiers]

We can simply rename it. I think axe.commons.aria.lookupTable would be fine. We're not accessing it directly in any of our checks or commons.

[dylanb]

What are the uses/use cases for use of this table? Might be better to expose those use cases as functions so we can change the implementation of the ARIA data in a backwards compatible way.

[marcysutton]

I've asked for more details.