Split the window_proxies in script thread into its own struct with
appropiate methods. ScriptThread allows to get an Rc to it.
HtmlIFrameElement, Window and WindowProxy now get the Rc on construction
from ScriptThread.
Testing: Just a refactor so should not change any behavior.
Fixes: Addresses part of https://github.com/servo/servo/issues/37969
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Signed-off-by: Narfinger <Narfinger@users.noreply.github.com>
This is part of the future work of implementing LazyDOMString as
outlined in https://github.com/servo/servo/issues/39479.
We use str() method or direct implementations on DOMString for these
methods. We also change some types.
Signed-off-by: Narfinger <Narfinger@users.noreply.github.com>
Testing: This is essentially just renaming a method and a type and
should not change functionality.
Signed-off-by: Narfinger <Narfinger@users.noreply.github.com>