Every embedded template has a cost: implementation, testing, maintenance, documentation, and support. To merit inclusion the requirement must be common and the implementation non-trivial. What you describe is neither.
{{- with $path := .Get 0 }}
{{- with $.Page.Resources.Get $path }}
{{- .Content | strings.TrimSpace | safeHTML }}
{{- else }}
{{- errorf "The %q shortcode was unable to find %s: see %s" $.Name $path $.Position }}
{{- end }}
{{- else }}
{{- errorf "The %q shortcode requires a single positional parameter, the path to the file within the current page bundle. See %s" .Name .Position }}
{{- end -}}
You can use either of these approaches to highlight the example code:
This is just one of several ways to do this, which is another reason to set the bar high for embedding a template: they are opinionated, and will rarely make everyone happy.