Development: Remove matchers.reload() on each request (#83829)
## What?
Re-apply #83720. It was reverted because of tests flaking significantly
more often.
Dug into this with @mischnic and @sokra yesterday and we found that it's
a race condition because of the two separate watchers. In
`setup-dev-bundler.ts` there's a Watchpack instance and Turbopack has
it's own watcher. The specific case where it caused flakes is when the
watchpack aggregate event runs before Turbopack's watcher has emitted a
change event. Since the watchpack aggregate callback emits `ADDED_PAGE`
/ `REMOVED_PAGE` over the websocket it would end up triggering the
browser `location.reload()` too early, before the Turbopack side has the
updated list of routes.
The right solution is to move the `matchers.reload()` and `ADDED_PAGE` /
`REMOVED_PAGE` events to where Turbopack emits that the list of routes
(entrypoints) has updated.
