Refactor Safe modifier (#29392)

After this PR: no need to play with the Safe/Escape tricks anymore. See
the changes for more details.

modules/templates/helper_test.go

@@ -4,6 +4,7 @@
 package templates
 
 import (
+	"html/template"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
@@ -56,3 +57,7 @@ func TestSubjectBodySeparator(t *testing.T) {
 func TestJSEscapeSafe(t *testing.T) {
 	assert.EqualValues(t, `\u0026\u003C\u003E\'\"`, JSEscapeSafe(`&<>'"`))
 }
+
+func TestHTMLFormat(t *testing.T) {
+	assert.Equal(t, template.HTML("<a>&lt; < 1</a>"), HTMLFormat("<a>%s %s %d</a>", "<", template.HTML("<"), 1))
+}