Support fallback roles

In axe-core 4.5 we stopped failing elements that use fallback roles in the role attribute. However many places in axe-core still assume fallback roles are not allowed. For example many rule selectors do something like `[role="button"]` to select elements with an explicit button role. That wouldn't work for elements with for example `role="button img"`, which will not match.

I think we need to do things for this ticket;

1. Go through the code base, and replace all uses of `.getAttribute('role')` / `.attr('role')` with `aria.getExplicitRole()`

2. The `fallback` flag of `aria.getRole()` and its related methods needs to be set to true, and tests need to be added in relevant places that are impacted by this.

3. Replace rule selectors that use `[role="??"]` with something that uses the explicit role. There are lots of ways we could do this, so we need to figure out what's the best way to do this first. Some ideas include allowing a custom `::axe/explicitRole('button')` selector, allowing the matches property to use `axe.commons.matches()` objects, or maybe adding an `option` object for matcher methods, and add an `explicit-role-matches` method.

Start by searching the codebase for .getAttribute('role'), .attr('role'), aria.getRole(), and selectors using [role="??"]. Read the related aria and rule tests before deciding how explicit-role matching should work; done means fallback roles are handled consistently, selectors use explicit roles, and impacted tests cover the behavior.

Written by the indexing model from the issue text.