feat: introduce syncMode to control the behavior of generating files

[kevinmarrec]

Description

Introduce the syncMode option to control the behavior of generating files.

Default to default

• append: only append the new components to the existing files.
• overwrite: overwrite the whole existing files with the current components.
• default: use append strategy when using dev server, overwrite strategy when using build.

Linked Issues

Resolves #804 (Please confirm ⚠️)

Linked Pull Requests

Closes #844

Additional context

Current logic is removeUnused === !this._server, which means only remove unused components when building and is dependent on vite mode ("Is there a dev server ?").

To prevent any breaking change, a default mode is required to follow current behavior, while append mode will always append which means also append with vite build.

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