script: Make timers per-process (#34581)

Before all timers were managed by the Constellation process, meaning
that they had to trigger IPC calls to be scheduled and fired. Currently,
timers are only used in the `ScriptThread`, so it makes sense that they
are per-process.

This change restores the timer thread functionality that existed before
avoided entirely. Completion is done using a callback that is sent to
the timer thread similarly to how fetch is done. This allows reusing the
existing task queue without making any new channels.

Fixes #15219.

Signed-off-by: Martin Robinson <mrobinson@igalia.com>

components/script/dom/dissimilaroriginwindow.rs

@@ -55,7 +55,6 @@ impl DissimilarOriginWindow {
                 global_to_clone_from.mem_profiler_chan().clone(),
                 global_to_clone_from.time_profiler_chan().clone(),
                 global_to_clone_from.script_to_constellation_chan().clone(),
-                global_to_clone_from.scheduler_chan().clone(),
                 global_to_clone_from.resource_threads().clone(),
                 global_to_clone_from.origin().clone(),
                 global_to_clone_from.creation_url().clone(),