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

tpl/template.go

@@ -165,10 +165,12 @@ var Context = struct {
 	SetDependencyManagerInCurrentScope func(context.Context, identity.Manager) context.Context
 	DependencyScope                    hcontext.ContextDispatcher[int]
 	Page                               hcontext.ContextDispatcher[page]
+	IsInGoldmark                       hcontext.ContextDispatcher[bool]
 }{
 	DependencyManagerScopedProvider: hcontext.NewContextDispatcher[identity.DependencyManagerScopedProvider](contextKey("DependencyManagerScopedProvider")),
 	DependencyScope:                 hcontext.NewContextDispatcher[int](contextKey("DependencyScope")),
 	Page:                            hcontext.NewContextDispatcher[page](contextKey("Page")),
+	IsInGoldmark:                    hcontext.NewContextDispatcher[bool](contextKey("IsInGoldmark")),
 }
 
 func init() {