This inserts a non-breaking space before backlinks to prevent them from being separated from footnote text.
Results in the following when text wraps:
```
1. Roses are red, violets are
blue ↩
```
Instead of this:
```
1. Roses are red, violets are blue
↩
```
This makes three changes to backlinks:
- Inserts a space before `<a href='…'>↩</a>` to make it look better
- Uses hexadecimal references (`&#x…;`) instead of decimal references for clarity
- Adds U+FE0E VARIATION SELECTOR 15 to the ↩ to suppress emojification on both iOS and Edge on Windows
If variation selector 15 isn't appended to the ↩, then the return arrow will show up as an emoji on iOS and Edge for Windows. The Pandoc project has already run into this quirk as documented on https://github.com/jgm/pandoc/issues/5469 and they've pushed a change for their Markdown processor already.
