Introduce non-user-observable Promise functions to use Promises internally

Introduce non-user-observable Promise functions to use Promises internally
https://bugs.webkit.org/show_bug.cgi?id=148118

Reviewed by Saam Barati.

To leverage the Promises internally (like ES6 Module Loaders), we add
the several non-user-observable private methods, like @then, @all. And
refactor the existing Promises implementation to make it easy to use
internally.

But still the trappable part remains. When resolving the promise with
the returned value, we look up the "then" function. So users can trap
by replacing "then" function of the Promise's prototype.
To avoid this situation, we'll introduce completely differnt promise
instances called InternalPromise in the subsequent patch[1].

No behavior change.

[1]: https://bugs.webkit.org/show_bug.cgi?id=148136

* builtins/PromiseConstructor.js:
(privateAll.newResolveElement):
(privateAll):
* runtime/JSGlobalObject.cpp:
(JSC::JSGlobalObject::init):
(JSC::JSGlobalObject::visitChildren): Deleted.
* runtime/JSGlobalObject.h:
(JSC::JSGlobalObject::promiseConstructor): Deleted.
(JSC::JSGlobalObject::promisePrototype): Deleted.
(JSC::JSGlobalObject::promiseStructure): Deleted.
* runtime/JSPromiseConstructor.cpp:
(JSC::JSPromiseConstructor::finishCreation):
* runtime/JSPromiseDeferred.cpp:
(JSC::callFunction):
(JSC::JSPromiseDeferred::resolve):
(JSC::JSPromiseDeferred::reject):
* runtime/JSPromiseDeferred.h:
* runtime/JSPromisePrototype.cpp:
(JSC::JSPromisePrototype::create):
(JSC::JSPromisePrototype::JSPromisePrototype):
* runtime/JSPromisePrototype.h:

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@188603 268f45cc-cd09-0410-ab3c-d52691b4dbfc