[devtools] restart server pending state (#80858)
This PR adds a pending state to the clear bundler cache & server
restart.
When the user clicks the restart server button, Next.js fetches
`/__nextjs_server_status` for the current server's execution ID. Then it
queries `/__nextjs_restart_dev` middleware to trigger the server
restart, then polls the `/__nextjs_server_status` path to confirm the
server execution ID differs, which means the new server is online.
When the server has restarted, reload the window.
Closes NEXT-4562
Closes NEXT-4501
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Co-authored-by: Jiachi Liu <inbox@huozhi.im>
