Support role=generic

[WilcoFiers]

Axe-core currently include generic in its list of roles. Even though ARIA says authors should not use it, they can, and from some quick testing it seems Firefox and Chrome allow it, and VO + Safari does seem to know to ignore it. More testing is probably needed, but even if it isn't fully supported it should be reported as not widely supported, instead of reporting it as an invalid role. It is a valid role.

[straker]

@chutchins25 Fixing this should be updating aria-roles.js file to add the generic role (the list is in alphabetical order) with the following definition:

{
  type: 'structure',
  prohibitedAttrs: ['aria-braillelabel', 'aria-brailleroledescription', 'aria-label,' aria-labelledby', 'aria-roledescription'],
  unsupported: true
}

Then adding tests to the aria-roles integration test to ensure a role of generic returns as incomplete (there's a comment block designating where it should go on the page).