We now apply MathML's default user agent style sheet along with other
default styles. This sheet is not mixed in with the other styles in
CSS/Default.css because it is a namespaced stylesheet and so has to
be its own sheet.
We got some errors while loading https://twinings.co.uk/ about this
interface missing, and it looked fairly simple so I sketched it out.
Note that I did leave some FIXMEs where it's not clear exactly which
metrics we should be returning.
This reduces the number of tasks to schedule, and the complexity of the
build system integrations for the BindingsGenerator. As a bonus, we move
the "only write if changed" feature into the generator to reduce the
build system load on generated files for this generator.
The idl file lists are used for two things:
1. As inputs for `generate_window_or_worker_interfaces`
2. In a loop in `generate_idl_bindings` and the loop variable
is passed to `rebase_path`
Both these cases can handle a normal fully-qualified GN path,
so there's no need for the "abspath".
No behavior change.
