should aria-hidden subtrees be ignored by clickButton, fillIn, etc?

```html

```

```elm
ProgramTest.clickButton "A"
```

Should the clickButton fail because its inside an `aria-hidden=true` element? I think that doesn't really make sense because isn't the button still visible on the page (even though hidden from accessibility tools) unless there is also CSS applied to hide it visually?

Start by reviewing the behavior of ProgramTest.clickButton, fillIn, and related helpers against the provided aria-hidden example. Decide whether accessibility-hidden subtrees should be excluded, then add coverage for the chosen behavior and document what the helpers should do.

Written by the indexing model from the issue text.