fix: use websocket to test server liveness before client reload

[hi-ogawa]

Description

• Closes Client pinging behind a proxy unexpected reload on websocket disconnect #13125
• Closes Support Cross-Origin-Opener-Policy and Cross-Origin-Embedder-Policy on hmr dev server #16536
• Supersedes/Closes fix: wait for restart behind reverse-proxy #17768
• Related (but this is a separate feature request) Avoid unnecessary reload after HMR WebSocket connection lost #5675

This PR makes waitForSuccessfulPing more robust by testing Vite server liveness based on websocket connection as suggested in #5675 (comment)

Testing #13125

• run playground e.g. pnpm -C playground/tailwind dev
• run proxy e.g. cloudflared tunnel --url http://localhost:5173/
• open a page from proxy e.g. https://arrow-lonely-looks-counsel.trycloudflare.com/
• stop playground server and see client keeps pinging (previously client full reloads here and ends up 502 page)
• start playground server and see client reloads automatically

Testing #16536 (this one is added as a test case)

• run playground pnpm -C playground/tailwind dev with a following server config

    server: {
      // different port for hmr websocket
      hmr: {
        port: 12345
      },
      // cross origin isolation headers
      headers: {
        "Cross-Origin-Embedder-Policy": "require-corp",
        "Cross-Origin-Opener-Policy": "same-origin"
      }

• stop playground server and see client keeps pinging
• start playground server and see client reloads (previously client fails to automatically full reload here)

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[hendrikheil]

My team applied these changes to vite locally and tried it with 5 different Nuxt 3 based applications running behind a traefik based https reverse proxy. This change massively improves the DX for us as we no longer have to constantly full-page reload our apps especially when vite is still booting.

I'd love to see this merged ❤️

Thanks @hi-ogawa, this gives us back so much productivity!