Template keep array iterator (#7412)

* Template keep array iterator

* Update Template.hx

Make it static to avoid creating too much instances.

* Update Template.hx

change `@:keep` to `@:ifFeature`

std/haxe/Template.hx

@@ -65,6 +65,9 @@ class Template {
 	**/
 	public static var globals : Dynamic = {};
 
+	// To avoid issues with DCE, keep the array iterator.
+	@:ifFeature("haxe.Template.run") static var hxKeepArrayIterator = [].iterator();
+
 	var expr : TemplateExpr;
 	var context : Dynamic;
 	var macros : Dynamic;