Previously if we encountered any attributes with a namespace other than
`xml` or `xmlns`, we treated it as a parse error. Now, allow it as long
as it's been declared in the current context.
We also handle errors more gracefully - instead of exploding if setting
the namespace fails, treat it as an error and carry on.
Names like ":hi", "wow:", or "a🅱️c" are invalid, so early-out instead
of searching our namespace stack for matching prefixes.
And also rename the function because it's relevant to attributes too.
While the code that did this referred to the HTML spec, other browsers
appear not to have this behavior when parsing XML, and it breaks a WPT
subtest.
This change does not appear to break any tests, and fixes 1 WPT subtest.
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
