Allow lazy, lazy-once and eager mode for import()
Fix a bug which caused context chunks to be merged when using chunk name
Allow to work in env where there is no Promise.resolve
Add specify chunk name feature for `import()` by following special comment block after the param:
import('./foo' /* webpackChunkName = "myChunkName" */)
Thus we can use chunk name like `requre.ensure` and avoid conflicts with the specification.