Change the IDL parser entry point to a static factory returning an
IDL::Module. Modules now own the parsed file identity and import graph,
with an optional reference to the file's real interface when one exists.
This is a step towards running the IDL generator on files without
an interface defined.
Start making IDL::Context represent the shared IDL world used during
code generation.
Move globally visible parsed IDL such as dictionaries, enums,
typedefs, callbacks, mixins, and partial declarations out of individual
Interface objects and into Context.
The main goal of this change is a step towards invoking the IDL
generator on every IDL file at once, rather than per interface.
In the meantime as standalone improvements, this lets code generation
resolve imported IDL types through the shared Context without copying
imported declarations onto each Interface. It also makes duplicate
local declarations unnecessary for imported shared types, since an
interface can reference an enum or dictionary owned by another
parsed IDL module without re-emitting it itself.
This adds parsing support for `partial interface mixin` as specified
in WebIDL. Partial mixins are merged into their corresponding mixins
before the mixins are resolved into interfaces.
Partial interfaces have the same name as the interface they extend, and
can appear in any order. In practice, we import the partial interfaces
into the main interface's IDL.
This adds support for async iterators of the form:
async iterable<value_type>;
async iterable<value_type>(/* arguments... */);
It does not yet support the value pairs of the form:
async iterable<key_type, value_type>;
async iterable<key_type, value_type>(/* arguments... */);
Async iterators have an optional `return` data property. There's not a
particularly good way to know what interfaces implement this property.
So this adds a new extended attribute, DefinesAsyncIteratorReturn, which
interfaces can use to declare their support.
This allows us to specify multiple base paths to look for imported IDL
files in. This will allow us to import IDL files from sources and from
the Build directory (i.e. for generated IDL files).
