feat: add generate command

[sis0k0]

PR Checklist

• The PR title follows our guidelines: https://github.com/NativeScript/NativeScript/blob/master/CONTRIBUTING.md#commit-messages.
• There is an issue for the bug/feature this PR is for. Feature Request: Use schematics for project transformations #3860
• You have signed the CLA.
• All existing tests are passing: https://github.com/NativeScript/nativescript-cli/blob/master/CONTRIBUTING.md#contribute-to-the-code-base
• Tests for the changes are included. The main functionality is implemented and tested in the @nativescript/schematics-executor package - repo.

tns generate

This PR introduces a new command - tns generate. The command uses schematics-executor for performing project modifications. The modifications are described with schematic rules, which are part of schematic collections. Each collection is distributed inside a node package. The default collection used by the tns generate command is @nativescript/schematics.

Usage

Arguments

The command has one required argument - the name of the executed schematic. For example, if we want to run the component schematic, the executed command is:

tns generate component

Schematic options

The executed schematic may have options. They are provided without the '--' prefix.
In the following example, the command generates a component using the component schematic and specifies the name and module options.

tns generate component name=my-component module=app 

The schematic options are specified with a schema that's different for each schematic. I couldn't find a way to execute the CLI command with dynamic options ( with --). That's why the schematic options are provided as arguments (without --) and then are validated against the schema by the schematic executor.

Specifying collection

The default collection is @nativescript/schematics. Different collection can be specified with the --collection option:

tns generate component --collection=@schematics/angular name=my-component module=app

Implements one of the features described in #3860.

[rosen-vladimirov]

After fixing the shrinkwrap

[sis0k0]

run ci