Verify correctness of the required browser features pages

[timvandermeij]

On https://github.com/mozilla/pdf.js/wiki/Required-Browser-Features we mention required browser features for PDF.js, but I have the feeling that not all of them are necessary nowadays since we moved to using more modern features over the years. Moreover, as indicated in #11950 (comment), some features may be missing such as range requests or async/await.

In short, we should verify which are still necessary and update the wiki page and the automated feature detection if possible.

[timvandermeij]

There is also the idea to replace the supported browsers overview with a verification based on which demo works; see #12170 (comment). If we use that, we might also consider dropping the required browser features page since I think it's not relevant then anymore.

[Snuffleupagus]

Given that this page hasn't received any meaningful updates since 2014[1], and that first of all fixing it and secondly keeping it up-to-date will take quite a bit of effort, I'd suggest that we move forward with #11954 (comment) instead.

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[1] There's been changes since then, but that's when the last feature-test was added.