Remove the remaining IE 11 polyfills
We really ought to settle on the *lowest* supported versions of various browsers[1], since that should allow even more clean-up, but given that https://github.com/mozilla/pdf.js/wiki/Frequently-Asked-Questions#faq-support *explicitly* lists IE 11 as unsupported after PDF.js version `2.6.347` there's a number of polyfills that are no longer needed.
Based on the MDN compatibility data, this patch thus removes the following polyfills:
- `String.prototype.startsWith()`, see https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/startsWith#Browser_compatibility
- `String.prototype.endsWith()`, see https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/endsWith#Browser_compatibility
- `String.prototype.includes()`, see https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/includes#Browser_compatibility
- `Array.prototype.includes()`, see https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/includes#Browser_compatibility
- `Array.from()`, see https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/from#Browser_compatibility
- `Object.assign()`, see https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/assign#Browser_compatibility
- `Math.log2()`, see https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Math/log2#Browser_compatibility
- `Number.isNaN()`, see https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number/isNaN#Browser_compatibility
- `Number.isInteger()`, see https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number/isInteger#Browser_compatibility
- `Map.prototype.entries()`, see https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map/entries#Browser_compatibility
- `Set.prototype.entries()`, see https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Set/entries#Browser_compatibility
- `WeakMap`, see https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WeakMap#Browser_compatibility
- `WeakSet`, see https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WeakSet#Browser_compatibility
- `Symbol`, see https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Symbol#Browser_compatibility
Finally, this patch also attempts to update the compatibility information for the remaining polyfills.
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[1] For example: It's questionable if Safari 9 should be listed as supported, given that the last release from that branch was in 2016.
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