markup/goldmark: Fix mangling of headers/links in render hooks

```bash

name                    old time/op    new time/op    delta
SiteWithRenderHooks-10    11.9ms ± 1%    11.9ms ± 1%    ~     (p=0.486 n=4+4)

name                    old alloc/op   new alloc/op   delta
SiteWithRenderHooks-10    11.2MB ± 0%    11.3MB ± 0%  +0.16%  (p=0.029 n=4+4)

name                    old allocs/op  new allocs/op  delta
SiteWithRenderHooks-10      145k ± 0%      145k ± 0%  +0.14%  (p=0.029 n=4+4)
```

Fixes #9504

1 files changed, 13 insertions, 3 deletions

diff --git a/markup/goldmark/convert.go b/markup/goldmark/convert.go
index dcaf8d3e1..c547fe1e0 100644
--- a/markup/goldmark/convert.go
+++ b/markup/goldmark/convert.go
@@ -47,8 +47,7 @@ import (
 // Provider is the package entry point.
 var Provider converter.ProviderProvider = provide{}
 
-type provide struct {
-}
+type provide struct{}
 
 func (p provide) New(cfg converter.ProviderConfig) (converter.Provider, error) {
 	md := newMarkdown(cfg)
@@ -199,10 +198,21 @@ func (b *bufWriter) Flush() error {
 
 type renderContext struct {
 	*bufWriter
-	pos int
+	positions []int
 	renderContextData
 }
 
+func (ctx *renderContext) pushPos(n int) {
+	ctx.positions = append(ctx.positions, n)
+}
+
+func (ctx *renderContext) popPos() int {
+	i := len(ctx.positions) - 1
+	p := ctx.positions[i]
+	ctx.positions = ctx.positions[:i]
+	return p
+}
+
 type renderContextData interface {
 	RenderContext() converter.RenderContext
 	DocumentContext() converter.DocumentContext