docs: assign code for each deprecation changes, provide option to opt-in

[antfu]

Assign code for each deprecations/future breaking changes we have, provide each a docs page to communicate with migration guides. (https://github.com/vitejs/vite/pull/17305/files#diff-dec483f20d5b5946a0879042e0894a3850672e347b12bfee87695d1b808bc82e)

For future deprecations, we provide config entries for early adopters to test the check the usage of those future-depreations features.

export default defineConfig({
  future: {
    deprecationWarnings: {
      serverModuleGraph: true,
      pluginHookHandleHotUpdate: true
    }
  }
})

Then users will get runtime warnings with stacktrace to locate the usage of those APIs:

[stackblitz]

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