The Window object is massive, so let's do the conversion to IDL step
by step. First up: getting rid of the manual constructor and prototype
definitions, which can be generated from an empty `interface Window`.
The condition for checking if there was already a response in recursive
fetch was accidentally flipped, always causing a null deref.
This made redirects crash for example.
This makes XHR now rely on Fetch, which allows it to correct send
Origin and Referer headers, CORS-preflight and filtering and many other
goodies.
The main thing that's missing is Streams, which means we can't properly
produce progress events or switch to the Loading ready state.
This also doesn't implement the Document responseType just yet.
Since we don't currently have streams, we didn't set length anywhere.
However, this is required by XHR's reliance on Fetch to get the total
number of bytes for the progress events.
This makes Fetch rely less on using main_thread_vm().current_realm(),
which relies on the dummy execution context if no JavaScript is
currently running.
This relied on pulling the current realm from the main thread VM, which
requires an execution context to be on the VM's stack. This heavily
relied on the dummy execution context that is always on the stack, for
example, when parsing the UA style sheets where no JavaScript is
running.
This requires Parser to be movable, so we remove the `default`
destructors from Parser and TokenStream, and give them both move
constructors. Since TokenStream only holds a reference to its tokens,
(and it needs to, to avoid copying when given eg a function's contents,)
we add a manual move constructor for Parser which creates a new
TokenStream from the new Parser's tokens, and then manually copies the
old TokenStream's state.
Instead of constructing a Tokenizer and then calling parse() on it, we
now call `Tokenizer::tokenize(...)` directly. (Renamed from `parse()`
because this is a Tokenizer, not a Parser.)
This class had slightly confusing semantics and the added weirdness
doesn't seem worth it just so we can say "." instead of "->" when
iterating over a vector of NNRPs.
This patch replaces NonnullRefPtrVector<T> with Vector<NNRP<T>>.
