Add @babel/plugin-proposal-decorators to transform

[LukeCSamuel-RV]

We make a lot of use of Typescript decorators in our code base. In Nuxt 2.14 they could be used in places outside of webpack module resolution, such as Nuxt modules. In Nuxt 2.15 they are no longer supported, because the babel instance bundled with Jiti doesn't have the @babel/plugin-proposal-decorators plugin.

I would propose that if opts.ts and ideally only when experimentalDecorators === true (from tsconfig), this plugin be added: _opts.plugins!.push([require('@babel/plugin-proposal-decorators'), { legacy: true }])

[pi0]

Hi @LukeCSamuel-RV. Thanks for issue it makes sense adding for typescript. Would you please open a pull request?

[tobiasdiez]

Could babel-plugin-transform-typescript-metadata also please be added so that the metadata added by these decorators can be used, say for dependency injection.

This would fix nuxt/typescript#494.

[NexZhu]

@jozsefsallai Could you please open a PR to add babel-plugin-transform-typescript-metadata?