Pass .RenderShortcodes' Page to render hooks as .PageInner

The main use case for this is to resolve links and resources (e.g. images) relative to the included `Page`.

A typical `include` would similar to this:

```handlebars
{{ with site.GetPage (.Get 0) }}
  {{ .RenderShortcodes }}
{{ end }}
```

And when used in a Markdown file:

```markdown
{{% include "/posts/p1" %}}
```

Any render hook triggered while rendering `/posts/p1` will get `/posts/p1` when calling `.PageInner`.

Note that

* This is only relevant for shortcodes included with `{{%` that calls `.RenderShortcodes`.
* `.PageInner` is available in all render hooks that, before this commit, received `.Page`.
* `.PageInner` will fall back to the value of `.Page` if not relevant and will always have a value.

Fixes #12356

markup/goldmark/convert.go

@@ -18,6 +18,7 @@ import (
 	"bytes"
 
 	"github.com/gohugoio/hugo-goldmark-extensions/passthrough"
+	"github.com/gohugoio/hugo/markup/goldmark/hugocontext"
 	"github.com/yuin/goldmark/util"
 
 	"github.com/gohugoio/hugo/markup/goldmark/codeblocks"
@@ -103,6 +104,7 @@ func newMarkdown(pcfg converter.ProviderConfig) goldmark.Markdown {
 		renderer.WithNodeRenderers(util.Prioritized(emoji.NewHTMLRenderer(), 200)))
 	var (
 		extensions = []goldmark.Extender{
+			hugocontext.New(),
 			newLinks(cfg),
 			newTocExtension(tocRendererOptions),
 		}