[webdav] Escape HTML entities by number

[CodingKoopa]

This pull request addresses issue #2599 by escaping the HTML entities by number, rather than the shorthand identifiers that strict XML parsers don't understand.

To obtain the list, I:

• Downloaded Blink's HTML entity list
• Removed entries at the bottom by hand that had two codepoints.
• Removed duplicate entries by replacing

^"(.+?)","U\+([0-9a-fA-F]{5})"\n"(.+?)","U\+(\2)"$

with

"$1","U+$2"`

• Converted the list to the source code format by replacing

^"(.+)?","U\+([0-9a-fA-F]{5})"$

with

        escapesec[$2] = "&#x$2;"; // $1

---

#2596 also fixes the aforementioned issue, which I admittedly didn't notice until submitting this PR. I believe they are sufficiently different approaches to the problem though.

This approach pollutes utils.cpp considerably, it may be better to split this off into a separate file.

Thanks!