Modernize benchmarks (#2132)

* Introduce benchmarks

lib/handlebars/compiler/javascript-compiler.js

@@ -173,6 +173,9 @@ JavaScriptCompiler.prototype = {
         }
       }
 
+      // Release AST/compiler references only needed during compilation for dedup
+      this.context.environments.length = 0;
+
       if (this.environment.usePartial) {
         ret.usePartial = true;
       }