Fix auto generated header ids so they don't contain e.g. hyperlink destinations (note)

This makes the header ids match the newly added dt ids.

Also make sure newlines are preserved in hooks' `.PlainText`.

Fixes #13405
Fixes #13410

markup/goldmark/internal/render/context.go

@@ -1,4 +1,4 @@
-// Copyright 2024 The Hugo Authors. All rights reserved.
+// Copyright 2025 The Hugo Authors. All rights reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
@@ -20,6 +20,7 @@ import (
 	"sync"
 
 	bp "github.com/gohugoio/hugo/bufferpool"
+	east "github.com/yuin/goldmark-emoji/ast"
 
 	htext "github.com/gohugoio/hugo/common/text"
 	"github.com/gohugoio/hugo/tpl"
@@ -282,6 +283,7 @@ func textPlainTo(c ast.Node, source []byte, buf *bytes.Buffer) {
 	if c == nil {
 		return
 	}
+
 	switch c := c.(type) {
 	case *ast.RawHTML:
 		s := strings.TrimSpace(tpl.StripHTML(string(c.Segments.Value(source))))
@@ -290,6 +292,11 @@ func textPlainTo(c ast.Node, source []byte, buf *bytes.Buffer) {
 		buf.Write(c.Value)
 	case *ast.Text:
 		buf.Write(c.Segment.Value(source))
+		if c.HardLineBreak() || c.SoftLineBreak() {
+			buf.WriteByte('\n')
+		}
+	case *east.Emoji:
+		buf.WriteString(string(c.ShortName))
 	default:
 		textPlainTo(c.FirstChild(), source, buf)
 	}