feat: Add partial quoting

- If you select a portion of the comment, `Quote reply` will not only
quote that portion and not copy paste the whole text as it previously
did. This is achieved by using the `@github/quote-selection` package.
- There's preprocessing to ensure Forgejo-flavored markdown syntax is
preserved.
- e2e test added.
- Resolves #1342

routers/api/v1/misc/markup_test.go

@@ -76,7 +76,7 @@ func TestAPI_RenderGFM(t *testing.T) {
 <ul>
 <li><a href="` + FullURL + `wiki/Links" rel="nofollow">Links, Language bindings, Engine bindings</a></li>
 <li><a href="` + FullURL + `wiki/Tips" rel="nofollow">Tips</a></li>
-<li>Bezier widget (by <a href="` + AppURL + `r-lyeh" rel="nofollow">@r-lyeh</a>) <a href="https://github.com/ocornut/imgui/issues/786" rel="nofollow">https://github.com/ocornut/imgui/issues/786</a></li>
+<li>Bezier widget (by <a href="` + AppURL + `r-lyeh" class="mention" rel="nofollow">@r-lyeh</a>) <a href="https://github.com/ocornut/imgui/issues/786" rel="nofollow">https://github.com/ocornut/imgui/issues/786</a></li>
 </ul>
 `,
 		// Guard wiki sidebar: special syntax