Keep footnote backlinks with text

[brief]

goldmark has https://github.com/yuin/goldmark/discussions in github. You should post only issues here. Feature requests and questions should be posted at discussions.

• [x] goldmark is fully compliant with the CommonMark. Before submitting issue, you must read CommonMark spec and confirm your output is different from CommonMark online demo.
  • [x] Extensions(Autolink without < >, Table, etc) are not part of CommonMark spec. You should confirm your output is different from other official renderers correspond with an extension.
• [x] goldmark is not dedicated for Hugo. If you are Hugo user and your issue was raised by your experience in Hugo, you should consider create issue at Hugo repository at first .

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Please answer the following before submitting your issue:

1. What version of goldmark are you using? 1.3.2
2. What version of Go are you using? 1.16
3. What operating system and processor architecture are you using? macOS Big Sur 11.3 Beta / x86_64
4. What did you do?

Created a footnote, like so:

This is a footnote[^1]

[^1]: Roses are red, violets are blue

5. What did you expect to see?

Expected the last word of the footnote and the backlink arrow to wrap together, as follows:

This is a footnote¹

---

1. Roses are red, violets are
blue ↩

PHP Markdown Extra inserts a non-breaking space before footnote backlinks instead of a normal space. I thought this was a recent change, but it has apparently done this since 2006.

6. What did you see instead?

The backlink arrow can break to a new line of its own on narrow screens:

This is a footnote¹

---

1. Roses are red, violets are blue
↩

7. Did you confirm your output is different from CommonMark online demo or other official renderer correspond with an extension? N/A, as this is for the footnote extension.

[yuin]

That makes sense.