Report outline storage retained by scripts, environments, module
namespace objects, iterator helpers, property name iterators, argument
objects, and error tracebacks. These objects keep vectors and maps that
can grow independently from their GC cell sizes.
Our existing implementation was checking if the generator step result
was `undefined` to indicate that the generator is complete. This is
not sufficient for an upcoming implementation of Iterator.concat, where
`undefined` is used as an incomplete iteration result.
Instead, let's have the Iterator prototype return an IterationResult to
explicitly indicate its completeness. As a result, the prototype also
looks more like the spec now.
- Create less GC pressure by making each `await` in async function skip
iteration result object allocation.
- Skip uncached `Object::get()` calls to extract `value` and `done` from
the iteration result object.
With this change, following function goes 30% faster on my computer:
```js
(async () => {
const resolved = Promise.resolve();
for (let i = 0; i < 5_000_000; i++) {
await resolved;
}
})();
```
Resulting in a massive rename across almost everywhere! Alongside the
namespace change, we now have the following names:
* JS::NonnullGCPtr -> GC::Ref
* JS::GCPtr -> GC::Ptr
* JS::HeapFunction -> GC::Function
* JS::CellImpl -> GC::Cell
* JS::Handle -> GC::Root
The main motivation behind this is to remove JS specifics of the Realm
from the implementation of the Heap.
As a side effect of this change, this is a bit nicer to read than the
previous approach, and in my opinion, also makes it a little more clear
that this method is specific to a JavaScript Realm.
