This is a continuation of the previous six commits.
The global object is only needed to return it if the execution context
stack is empty, but that doesn't seem like a useful thing to allow in
the first place - if you're not currently executing JS, and the
execution context stack is empty, there is no this value to retrieve.
This is a continuation of the previous five commits.
A first big step into the direction of no longer having to pass a realm
(or currently, a global object) trough layers upon layers of AOs!
Unlike the create() APIs we can safely assume that this is only ever
called when a running execution context and therefore current realm
exists. If not, you can always manually allocate the Error and put it in
a Completion :^)
In the spec, throw exceptions implicitly use the current realm's
intrinsics as well: https://tc39.es/ecma262/#sec-throw-an-exception
The [Replaceable] attribute "indicates that setting the corresponding
property on the platform object will result in an own property with the
same name being created on the object which has the value being
assigned. This property will shadow the accessor property corresponding
to the attribute, which exists on the interface prototype object."
(https://heycam.github.io/webidl/#Replaceable)
The spec doesn't tell how exactly this is supposed to be done, but other
engines just have a setter as well that just redefines the property
as a data descriptor when called, and returns undefined.
It's bound to the property name and requires an object of the correct
type, so I mirrored these constraints here. Storing the setter and
calling it multiple times will therefore just work.
Implementing this in the wrapper generator is left as an exercise for
the reader, this is going to be used in WindowObject, which isn't
generated from IDL yet.
