Auto merge of #14260 - asajeffrey:constellation-event-loops, r=Ms2ger

Rename ScriptChan in constellation to EventLoop

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We currently have a type `ScriptChan` in the constellation, which is named after its implementation rather than its semantics. In the spec, the nearest concept seems to be event loop https://html.spec.whatwg.org/multipage/#event-loop.

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- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes do not require tests because renaming.

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components/constellation/lib.rs

@@ -43,6 +43,7 @@ extern crate style_traits;
 extern crate webrender_traits;
 
 mod constellation;
+mod event_loop;
 mod pipeline;
 #[cfg(not(target_os = "windows"))]
 mod sandboxing;