Clean up the css related template funcs package structure

Deprecate and move:

* resources.ToCSS => css.SASS
* resources.PostProcess => css.PostProcess
* resources.Babel => js.Babel

Updates #12618

tpl/js/init.go

@@ -31,6 +31,11 @@ func init() {
 			Context: func(cctx context.Context, args ...any) (any, error) { return ctx, nil },
 		}
 
+		ns.AddMethodMapping(ctx.Babel,
+			[]string{"babel"},
+			[][2]string{},
+		)
+
 		return ns
 	}