Editorial: completion reform for JavaScript AOs

As part of the tc39/ecma262#2547 the JavaScript specification has reformed how it deals with Completion Records, and thus what abstract operations can return. See tc39/ecma262#253 (comment) for a brief description of when to use ? vs. ! vs. nothing at all.

Additional minor fixes:

* Replace uses of ObjectCreate (which no longer exists) with OrdinaryObjectCreate.
* Replace "Rethrow any exceptions" with the ? syntax.
* Use ? with GetFunctionRealm, which can throw due to revoked proxies.