Moving WebGL execution into the Compositor needs a serializable command
stream and a client-side proxy that can queue commands before sending
them over IPC. The existing generator metadata only described direct GL
wrappers, so generated code could not distinguish async commands from
sync calls or object factory methods.
This teaches the WebGL metadata and generators about command streams and
adds the unused LibWeb proxy/list types. No rendering behavior changes
yet; the later host wiring can build on these generated interfaces
without mixing the metadata churn into that commit.
