This reduces the recompilation cascade when Document.h is modified,
cutting off the transitive path through ~30 SVG element headers.
Move the inline try_resolve_url_to() template body in
SVGGraphicsElement.h to a non-template helper in the .cpp file to
avoid needing Document.h and ShadowRoot.h in the header.
Add explicit includes to files that relied on the transitive dependency.
Previously, referencing an element that eventually pointed back to
the original <use> element would cause a stack overflow.
We now look at the referenced element and follow every <use> element
in its subtree and aim to detect any duplicates. If so, we consider
that referenced element invalid.
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
We currently have 2 virtual methods to inform DOM::Element subclasses
when an attribute has changed, one of which is spec-compliant. This
patch removes the non-compliant variant.
