Use WebIDL::set_prototype_from_new_target() in the handwritten Audio,
Image, and Option legacy factory constructors so subclassed
construction uses the correct prototype.
This corresponds to step 1.6 of:
https://webidl.spec.whatwg.org/#legacy-factory-functions
Prevents observably calling Trusted Types, which can run arbitrary JS,
cause crashes due to use of MUST and allow arbitrary JS to modify
internal elements.
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
