feat(Schematics): extend/add to a schematic from another collection

[mohammedzamakhan]

Bug Report or Feature Request (mark with an x)

- [x] feature request

Area

- [x] schematics

Desired functionality

Right now I know we can do something like

component: {
    extends: '@schematics/angular'
}

But I don't think we can add functionality upon this

Mention any other details that might be useful

USE CASE:

Example: I want to create a schematic that would be running like ng new angular-jest --collection jest_collection_name"

and it would create a new angular project using @schematics/angular, and then add more files that would make this application support running tests using jest.

[mohammedzamakhan]

@Brocco

[geneshap]

create aliases for all angular schematics in your own collection (note that alias for just application is not enough since it in turn uses other schematics). then from your own custom schematic return something like this:
export default function (options: any): Rule { return chain([ schematic('application', { style: 'scss', routing: true, directory: options.name, name: options.name }), mergeWith(apply(url('./files'), [ template({ name: options.name, }), ])), ]);

[hansl]

Dupe of #34