Remove dependency on non-standard Array.some() and Array.filter()

Remove dependency on non-standard Array.some() and Array.filter()

Also replaces the deprecated DOMQuad.bounds.

Firefox 70 will remove[1] non-standard Array generics[2][3]. These were
identified using the following shell pipeline:
  cd VimFx/extension
  grep -rn 'Array\.' | grep -v '\.isArray\|\.of\|\.from\|\.prototype'

[1]: https://bugzilla.mozilla.org/show_bug.cgi?id=1558914
[2]: https://www.fxsitecompat.dev/en-CA/docs/2019/non-standard-array-generics-have-been-deprecated/
[3]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array#Array_generic_methods