Avoid going through ExecState for VM when we already have it (in some places.)

Avoid going through ExecState for VM when we already have it (in some places.)
<https://webkit.org/b/129554>

Tweak some places that jump through unnecessary hoops to get the VM.
There are many more like this.

Reviewed by Sam Weinig.

* runtime/JSObject.cpp:
(JSC::JSObject::putByIndexBeyondVectorLength):
(JSC::JSObject::putDirectIndexBeyondVectorLength):
* runtime/ObjectPrototype.cpp:
(JSC::objectProtoFuncToString):

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@164925 268f45cc-cd09-0410-ab3c-d52691b4dbfc