Adopt consensus changes from tc39/proposal-explicit-resource-management#180

Author: rbuckton

spec.html

@@ -7391,6 +7391,12 @@ <h1>
           1. Let _method_ be ? GetMethod(_V_, @@asyncDispose).
           1. If _method_ is *undefined*, then
             1. Set _method_ to ? GetMethod(_V_, @@dispose).
+            1. Let _closure_ be a new Abstract Closure with no parameters that captures _method_ and performs the following steps when called:
+              1. Let _O_ be the *this* value.
+              1. Perform ? Call(_method_, _O_).
+              1. Return *undefined*.
+            1. NOTE: This function is not observable to user code. It is used to ensure that a Promise returned from a synchronous `@@dispose` method will not be awaited.
+            1. Return CreateBuiltinFunction(_closure_, 0, *""*, « »).
         1. Else,
           1. Let _method_ be ? GetMethod(_V_, @@dispose).
         1. Return _method_.