Represent WebIDL C++ types with a single CppType model that tracks
nullability, optional presence, and contained storage.
GC-like values now use GC::Ref/GC::Ptr directly, while containers choose
"plain", "Root", or "Conservative" container types depending on what
they contain. For example, sequence<Element> becomes a RootVector of
GC::Ref values, while sequence<SomeDictionary> becomes a
ConservativeVector only when the dictionary contains GC-like values.
This moves the generated bindings away from wrapping GC values in
GC::Root by default.
This has broad fallout as the types passed to interfaces for GC
objects changes almost fully across the board.
Previously we were inconsistent by generating code for enum definitions
but not generating code for dictionaries. With future changes to the
IDL generator to expose helpers to convert to and from IDL values
this produced circular depdendencies. To solve this problem, also
generate the dictionary definitions in bindings headers.
Our structured serialization implementation had its own bespoke encoder
and decoder to serialize JS values. It also used a u32 buffer under the
hood, which made using its structures a bit awkward. We had previously
worked around its data structures in transferable streams, which nested
transfers of MessagePort instances. We basically had to add hooks into
the MessagePort to route to the correct transfer receiving steps, and
we could not invoke the correct AOs directly as the spec dictates.
We now use IPC mechanics to encode and decode data. This works because,
although we are encoding JS values, we are only ultimately encoding
primitive and basic AK types. The resulting data structures actually
enforce that we implement transferable streams exactly as the spec is
worded (I had planned to do that in a separate commit, but the fallout
of this patch actually required that change).
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
