feat(renderer): use a comment instead of an element when stamping out template>` elements

Originally authored by @tbosch, this reverts the revert commit
e274ff8a69.

Closes #4805

modules/benchmarks/e2e_test/naive_infinite_scroll_spec.ts

@@ -9,7 +9,7 @@ describe('ng2 naive infinite scroll benchmark', function() {
   it('should not throw errors', function() {
     browser.get(URL);
     var expectedRowCount = 18;
-    var expectedCellsPerRow = 28;
+    var expectedCellsPerRow = 27;
     var allScrollItems = 'scroll-app #testArea scroll-item';
     var cells = `${ allScrollItems } .row *`;
     var stageButtons = `${ allScrollItems } .row stage-buttons button`;