[GITEA] Revert "Make user-content-* consistent with github (go-gitea#26388)"

Refs: https://codeberg.org/forgejo/forgejo/issues/1943

This reverts commit d41aee1.

(cherry picked from commit d29ec91e91362b0657edee631f12cf1d55ba7a2c)
(cherry picked from commit a0f5a9750e81c5e3992365f61b8cb9ab99413139)
(cherry picked from commit 26bfc3b)
(cherry picked from commit 59f57a1bc9d97d76319a6e2d8b7a336a9a480bb4)
(cherry picked from commit ce3b73a033d6f8b617b01f4f9fb33d70abf714aa)
(cherry picked from commit 2c426c28af18b69305bc8d71c389f21432fd8c3d)
(cherry picked from commit 155a08bca71cb90e753b73cbcd522e4f5064d980)
(cherry picked from commit 8934fd895c875135b4eb41dc2a1e2e456faf10da)

Author: earl-warren

modules/markup/common/footnote.go

@@ -29,12 +29,17 @@ func CleanValue(value []byte) []byte {
 	value = bytes.TrimSpace(value)
 	rs := bytes.Runes(value)
 	result := make([]rune, 0, len(rs))
+	needsDash := false
 	for _, r := range rs {
-		if unicode.IsLetter(r) || unicode.IsNumber(r) || r == '_' || r == '-' {
+		switch {
+		case unicode.IsLetter(r) || unicode.IsNumber(r) || r == '_':
+			if needsDash && len(result) > 0 {
+				result = append(result, '-')
+			}
+			needsDash = false
 			result = append(result, unicode.ToLower(r))
-		}
-		if unicode.IsSpace(r) {
-			result = append(result, '-')
+		default:
+			needsDash = true
 		}
 	}
 	return []byte(string(result))