fix: legacy no emit worker

[poyoho]

Description

fix: #9305

Additional context

In the generateBundle hook,
we'll delete the assets from the legacy bundle to avoid emitting duplicate assets.
But that's still a waste of computing resource.
So we add this flag to avoid emitting the asset in the first place whenever possible.

worker as assets will delete by plugin-legacy. So make the worker emit asset like emit css, avoid delete worker asset in legacy building.

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What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

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