feat: add resolve.alias and deprecate source.alias

[chenjiahan]

Summary

Rename source.alias to resolve.alias, the renamed API is consistent with Rspack/Vite and more intuitive.

export default {
- source: {
+ resolve: {
    alias: {}
  },
}

source.alias is deprecated, but it is still available and we plan to remove it in Rsbuild 2.0.

Related Links

https://rspack.dev/config/resolve#resolvealias

Checklist

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

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