Accessible name: Consider empty attributes as empty name

[WilcoFiers]

This was brought up in ACT: act-rules/act-rules.github.io#1861

<input type="image" alt="" title="hello world">

The above example in Firefox gets hello world as its accessible name, but in Chrome the name is empty, and so axe-core should fail this example.

Since the question's going to come up, this is different from how aria-label works. If you put an empty aria-label, Chrome will go onto the next name calculation method. It does not do that for the empty alt attribute case. We'll need to look at other scenarios here too. I don't know how this works for img elements for example, or input[type=button] with an empty value.

Before we can work on this we'll need to research similar cases, figure out where else this kind of logic applies.