Otherwise, the load event will block the original document until GC
runs.
Without this, media-load-task-after-adoption.html would wait for the
idle timeout to trigger a garbage collection, which could sometimes
cause the test to time out entirely.
Make Variant::visit reject typed visitor overloads that cannot be
called for any variant alternative. This catches stale visitors after a
variant payload type changes instead of falling through to a generic
overload.
Update fetch body consumers that still expected ByteBuffer after the
body payload moved to Core::ImmutableBytes.
Replace the spin_until in SVGScriptElement::process_the_script_element
with an async fetch that mirrors HTMLScriptElement's mark_as_ready
pattern. External SVG scripts now fetch and execute asynchronously,
matching Chromium's behavior.
For HTML-embedded SVG scripts, the parser pauses via the existing
schedule_resume_check infrastructure, extended to support SVG scripts
through a new pending_parsing_blocking_svg_script slot on Document.
For top-level XML/SVG documents, scripts execute when their fetch
completes; the load event is delayed via DocumentLoadEventDelayer which
the existing XMLDocumentBuilder::document_end already waits on.
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
