fix(plugin-legacy): fail to get the fileName

[dragonHandsome]

fileName could not be obtained in the bundle argument of the writeBundle hook, see: https://rollupjs.org/guide/en/#writebundle

Description

Additional context

---

What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

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[Shinigami92]

Was name always wrong here? Or can we use something like name || fileName 🤔

[dragonHandsome]

I expect the bundle's key to be fileName, because rollup.d.ts is written that way. In fact it's pretty much what I expected, except for 'polyfills-legacy ' chunk. see:
print: assets [
'assets/index-legacy.fc12ec77.js',
'assets/vendor-legacy.2384e447.js',
'polyfills-legacy',
'assets/cut.bd8e1359.png',
'assets/index.4f943797.js',
'assets/vendor.92adb1a9.js',
'assets/vendor.6ff1d4f6.css',
'assets/index.1a175568.css',
'index.html'
]
code: writeBundle(options, bundle) {
Object.keys(bundle).map(fileName => {
// fileName.startsWith('assets') &&
assets.push(fileName)
// assets.push(bundle[fileName].fileName)
})
},
closeBundle() {
console.log('assets', assets)
}