feat(cli): Generator support async

[xierenyuan]

In some cases, asynchronous operations in the generator will cause the build to fail, so I hope that the generator can support async

demo

const packageJson = require('package-json')

const pkgConfig = {
  registryUrl: 'todo'
}

module.exports = async (api, options, rootOptions) => {
   const pkg1 = await packageJson('todo pkg', pkgConfig)
   api.render('./template', rootOptions)
   
    // todo...

    api.extendPackage({
	devDependencies: {
	     'todo pkg': pkg1.version
	}
    })
}

[Akryum]

Maybe use async with a for loop?

[rikbrowning]

Can we not do something like:

Suggested change

	return new Promise((resolve, reject) => {
	return Promise.all(this.plugins.map(({ id, apply, options }) => {
	const api = new GeneratorAPI(id, this, options, rootOptions)
	return apply(api, options, rootOptions, invoking)
	}))

[vue-bot]

Hey @xierenyuan, thank you for your time and effort spent on this PR, contributions like yours help make Vue better for everyone. Cheers! 💚