Reusing variable names between module scripts in entry html causes devServer to fail

[OliverTsang]

Describe the bug

I have an entry html (such as index.html) like this:

<script type="module">
  const el = document.createElement('span');
  el.innerHTML = 'hello ';
  document.body.appendChild(el);
</script>

<script type="module">
  const el = document.createElement('span');
  el.innerHTML = 'world';
  document.body.appendChild(el);
</script>

I reused variable names between different module scripts, and then i ran vite and got an error:

The symbol "el" has already been declared

This error will cause the devServer to fail to start. The current workaround is to not reuse variable names between html module scripts.

I think this is a bug, because if you access an html directly in the browser, you can use the same variable name in different module scripts.

Reproduction

https://stackblitz.com/edit/vitejs-vite-kabw2t?file=package.json&terminal=dev

System Info

System:
    OS: macOS 10.15.5
    CPU: (8) x64 Intel(R) Core(TM) i7-8557U CPU @ 1.70GHz
    Memory: 201.05 MB / 16.00 GB
    Shell: 5.7.1 - /bin/zsh
  Binaries:
    Node: 14.4.0 - /usr/local/bin/node
    Yarn: 1.22.17 - /usr/local/bin/yarn
    npm: 6.14.4 - /usr/local/bin/npm
  Browsers:
    Chrome: 98.0.4758.80
    Safari: 13.1.1
  npmPackages:
    vite: ^2.7.2 => 2.8.0

Used Package Manager

npm

Logs

✘ [ERROR] The symbol "el" has already been declared

    html:/home/projects/vitejs-vite-kabw2t/index.html:8:12:
      8 │       const el = document.createElement('span');
        ╵             ~~

  The symbol "el" was originally declared here:

    html:/home/projects/vitejs-vite-kabw2t/index.html:3:12:
      3 │       const el = document.createElement('span');
        ╵             ~~

  vite:resolve 0.80ms /main.js -> /home/projects/vitejs-vite-kabw2t/main.js +0ms
error when starting dev server:
Error: Build failed with 1 error:
html:/home/projects/vitejs-vite-kabw2t/index.html:8:12: ERROR: The symbol "el" has already been declared
    at failureErrorWithLog (/home/projects/vitejs-vite-kabw2t/node_modules/esbuild/lib/main.js:1557:15)
    at eval (/home/projects/vitejs-vite-kabw2t/node_modules/esbuild/lib/main.js:1215:28)
    at runOnEndCallbacks (/home/projects/vitejs-vite-kabw2t/node_modules/esbuild/lib/main.js:1005:63)
    at buildResponseToResult (/home/projects/vitejs-vite-kabw2t/node_modules/esbuild/lib/main.js:1213:7)
    at eval (/home/projects/vitejs-vite-kabw2t/node_modules/esbuild/lib/main.js:1322:14)
    at eval (/home/projects/vitejs-vite-kabw2t/node_modules/esbuild/lib/main.js:637:9)
    at handleIncomingPacket (/home/projects/vitejs-vite-kabw2t/node_modules/esbuild/lib/main.js:734:9)
    at Socket.readFromStdout (/home/projects/vitejs-vite-kabw2t/node_modules/esbuild/lib/main.js:604:7)
    at Socket.EventEmitter.emit (https://vitejs-vite-kabw2t.w.staticblitz.com/blitz.05388ae171e3a0a12539f1efbda0fa1189d4f549.js:6:130023)
    at addChunk (https://vitejs-vite-kabw2t.w.staticblitz.com/blitz.05388ae171e3a0a12539f1efbda0fa1189d4f549.js:6:526052)

Validations

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• Read the Contributing Guidelines.
• Read the docs.
• Check that there isn't already an issue that reports the same bug to avoid creating a duplicate.
• Make sure this is a Vite issue and not a framework-specific issue. For example, if it's a Vue SFC related bug, it should likely be reported to https://github.com/vuejs/core instead.
• Check that this is a concrete bug. For Q&A open a GitHub Discussion or join our Discord Chat Server.
• The provided reproduction is a minimal reproducible example of the bug.

[OliverTsang]

I try to fix it in #6818, I hope this PR will help with this issue. Thx!