This change is reviewable per commits:
In first commit we added `&mut JSContext` to `run_box` (it is very hard
to bring `&mut JSContext` to `remove_script_and_layout_blocker`).
In second commit we pass `&mut JSContext` to `run_once`.
In third commit we added support for accepting `&mut JSContext` in
closures of `task!` macro and lastly we demo new macro invocations (to
ensure they actually compile)
Testing: Just refactor, but should be covered by WPT
Part of #40600
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Signed-off-by: sagudev <16504129+sagudev@users.noreply.github.com>