We previously had PropertyOwningCSSStyleDeclaration and
ResolvedCSSStyleDeclaration, representing the current style properties
and resolved style respectively. Both of these were the
CSSStyleDeclaration type in the CSSOM. (We also had
ElementInlineCSSStyleDeclaration but I removed that in a previous
commit.)
In the meantime, the spec has changed so that these should now be a new
CSSStyleProperties type in the CSSOM. Also, we need to subclass
CSSStyleDeclaration for things like CSSFontFaceRule's list of
descriptors, which means it wouldn't hold style properties.
So, this commit does the fairly messy work of combining these two types
into a new CSSStyleProperties class. A lot of what previously was done
as separate methods in the two classes, now follows the spec steps of
"if the readonly flag is set, do X" instead, which is hopefully easier
to follow too.
There is still some functionality in CSSStyleDeclaration that belongs in
CSSStyleProperties, but I'll do that next. To avoid a huge diff for
"CSSStyleDeclaration-all-supported-properties-and-default-values.txt"
both here and in the following commit, we don't apply the (currently
empty) CSSStyleProperties prototype yet.
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
