chore(plugin-less): use Rslib to bundle

[chenjiahan]

Summary

Use Rslib to bundle @rsbuild/plugin-less.

TODO:

• getLessLoaderOptions should not be marked as deprecated after bundling.
• The target should not become es5 when using syntax: https://github.com/web-infra-dev/rslib/blob/ed9fe5b0760822e703d9703d5ec31dc86ead2e5f/packages/core/src/config.ts#L569

Related Links

https://github.com/web-infra-dev/rslib

Checklist

• Tests updated (or not required).
• Documentation updated (or not required).

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