Add Dart Sass support

But note that the Dart Sass Embedded Protocol is still in beta (beta 5), a main release scheduled for Q1 2021.

Fixes #7380
Fixes #8102

markup/pandoc/convert.go

@@ -16,6 +16,7 @@ package pandoc
 
 import (
 	"github.com/cli/safeexec"
+	"github.com/gohugoio/hugo/htesting"
 	"github.com/gohugoio/hugo/identity"
 	"github.com/gohugoio/hugo/markup/internal"
 
@@ -74,5 +75,8 @@ func getPandocExecPath() string {
 
 // Supports returns whether Pandoc is installed on this computer.
 func Supports() bool {
+	if htesting.SupportsAll() {
+		return true
+	}
 	return getPandocExecPath() != ""
 }