The window title is derived based on the current document's `<h1>` heading. Such
headings may contain hidden/non-visible content (e.g. textual name of font
ligatures: `<i class="material-icons">link</i>`) that should not be included in
the title.
This commit fixes this by using `innerText` (instead of `textContent`) to
extract the visible text from the `<h1>` heading. It will still fall back to
`textContent` on browsers that do not support `innerText` (e.g. Firefox 44).
Fixes#17732
`innerText` is not supported in Firefox prior to v45. In most cases (at least
the ones we are interested in), `innerText` and `textContent` work equally well,
but `textContent` is more performant (as it doesn't require a reflow).
From [MDN][1] on the differences of `innerText` vs `textContent`:
> - [...]
> - `innerText` is aware of style and will not return the text of hidden
> elements, whereas `textContent` will.
> - As `innerText` is aware of CSS styling, it will trigger a reflow, whereas
> `textContent` will not.
> - [...]
[1]: https://developer.mozilla.org/en-US/docs/Web/API/Node/textContent#Differences_from_innerTextFixes#17585
