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, we only supported very basic numbers and a single level of
text positioning support in the `x`, `y`, `dx` and `dy` attributes in
`<text>` and `<tspan>` SVG elements.
This improves our support for them in the following ways:
* Any `length-percentage` or `number` type value is accepted;
* Nested `<text>` and `<tspan>` use the 'current text position'
concept to determine where the next text run should go;
* We expose the attributes' values through the API.
Though we still do not support:
* Applying the `rotate` attribute;
* Applying transformations on a per-character basis.
* Proper horizontal and vertical glyph advancing (we just use the path
bounding box for now).
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.
