Object-alt rule should ignore objects that don't load things

[WilcoFiers]

The following is from an ACT inapplicable example, axe shouldn't fail this:

<object data="/invalid/url/index.html">
  <img src="/WAI/content-assets/wcag-act-rules/test-assets/shared/w3c-logo.png" alt="W3C logo" />
</object>

I'm not sure how to directly detect whether an object loaded something, but detecting that its pass-through content is displayed can easily be done by just checking that it's children have a position, for example by calling getClientRects() on them. There are probably other ways to do it too.

To do this we'll probably need a new matches method for objects that can filter out objects which show their content.

[padmavemulapati]

Validated with the latest axe-core develop branch code base,
for the test script:

<object data="/invalid/url/index.html">
  <img src="/WAI/content-assets/wcag-act-rules/test-assets/shared/w3c-logo.png" alt="W3C logo" />
</object>

object-alt rule is appearing in inapplicable , not failing