Remove mutability from parser/tokenizer APIs.

[jdm]

This is incompatible with a re-entrant parsing algorithm which is required by the web platform's document.write API.

[jdm]

FYI @Taym95

[Taym95]

FYI @Taym95

Thanks, Should I close the other PR? lets me knew is you need help here in clean up.

[jdm]

This change is necessary to minimize the scope of refcell borrows that are passed as arguments to the macro.

[jdm]

FYI @Taym95

Thanks, Should I close the other PR? lets me knew is you need help here in clean up.

We can still merge the other PR, but we should remove all uses of &mut BufferQueue from the codebase in it (and uses like &mut input).

[jdm]

Ok, the code's cleaned up and commits are split into:

1. mechanical changes - lots of removing &mut self from methods and adding Cell/RefCell
2. new APIs needed by Support HTML parser reentrancy servo#32820
3. functional changes - the TreeSink API for obtaining an element's name relies on borrowed data in ways that do not play nicely with naive usage of RefCell to store the element name data (ExpandedName docs)
4. (and remaining commits) getting CI to pass

[jdm]

@Taym95 Would you like to review this?

[Taym95]

I've reviewed all the changes, and everything looks good to me!