Add GetPromiseIsHandled to JSAPI via patch

Ref: #150 (comment)

Author: CYBAI

etc/patches/is_handled.patch

@@ -0,0 +1,36 @@
+diff --git a/mozjs/js/src/jsapi.cpp b/mozjs/js/src/jsapi.cpp
+index 94ef1b3ed..06be95062 100644
+--- a/mozjs/js/src/jsapi.cpp
++++ b/mozjs/js/src/jsapi.cpp
+@@ -5162,6 +5162,14 @@ JS::GetPromiseResult(JS::HandleObject promiseObj)
+     return promise->state() == JS::PromiseState::Fulfilled ? promise->value() : promise->reason();
+ }
+ 
++JS_PUBLIC_API(bool)
++JS::GetPromiseIsHandled(JS::HandleObject promiseObj)
++{
++    PromiseObject* promise = &promiseObj->as<PromiseObject>();
++    MOZ_ASSERT(promise->state() == JS::PromiseState::Rejected);
++    return !promise->isUnhandled();
++}
++
+ JS_PUBLIC_API(JSObject*)
+ JS::GetPromiseAllocationSite(JS::HandleObject promise)
+ {
+diff --git a/mozjs/js/src/jsapi.h b/mozjs/js/src/jsapi.h
+index c7f92e273..5c5e9abc5 100644
+--- a/mozjs/js/src/jsapi.h
++++ b/mozjs/js/src/jsapi.h
+@@ -4390,6 +4390,12 @@ GetPromiseID(JS::HandleObject promise);
+ extern JS_PUBLIC_API(JS::Value)
+ GetPromiseResult(JS::HandleObject promise);
+ 
++/**
++ * Returns thhe given Promise's internal slot of `isHandled`.
++ */
++extern JS_PUBLIC_API(bool)
++GetPromiseIsHandled(JS::HandleObject promise);
++
+ /**
+  * Returns a js::SavedFrame linked list of the stack that lead to the given
+  * Promise's allocation.