Auto merge of #12560 - djc:layout-threads-hoist, r=emilio

Hoist retrieval of layout_threads from opts into Constellation

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This makes the lower-level crates less dependent on `util::opts`.

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- [X] `./mach test-tidy` does not report any errors
- [ ] These changes fix #__ (github issue number if applicable).

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- [ ] There are tests for these changes OR
- [X] These changes do not require tests because refactoring only

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components/script/script_thread.rs

@@ -1142,6 +1142,7 @@ impl ScriptThread {
             pipeline_port,
             layout_to_constellation_chan,
             content_process_shutdown_chan,
+            layout_threads,
         } = new_layout_info;
 
         let layout_pair = channel();
@@ -1158,6 +1159,7 @@ impl ScriptThread {
             script_chan: self.control_chan.clone(),
             image_cache_thread: self.image_cache_thread.clone(),
             content_process_shutdown_chan: content_process_shutdown_chan,
+            layout_threads: layout_threads,
         };
 
         let context = self.root_browsing_context();