Separate user/author defined options from yeoman internal options

[desidia26]

Feature:
Currently to access user supplied options/options that the author of the generator defines, that author must reference the this.options object. This object contains what looks to be yeoman internal data such as

`

env: Environment {

_events: [Object: null prototype] { error: [Function] },

_eventsCount: 1,

_maxListeners: undefined,

arguments: [],

options: {},

adapter: TerminalAdapter { promptModule: [Function] },

store: Store {

  _generators: [Object],

  _meta: [Object],

  _packagesPaths: [Object],

  _packagesNS: [Array]

},

runLoop: Queue {

  queueNames: [Array],

  __queues__: [Object],

  _maxListeners: 0

},

sharedFs: Store {

  _events: [Object: null prototype] {},

  _eventsCount: 0,

  _maxListeners: 0

},

lookups: [ '.', 'generators', 'lib/generators' ],

aliases: [ [Object] ],

sharedOptions: { sharedData: {} }

`

It would be helpful to separate these from user/author defined options so that option validation could be done more easily.

Use case: I have a generator where I wish to check and see if the user has passed an argument that I don't account for, and notify them.

[mshima]

It's possible to pass environments defined options on another constructor parameter to Generator.
https://github.com/yeoman/environment/blob/5c77b3ed017ab5b3f3e4aafe544f8a2b8b1d60a6/lib/environment.js#L547-L555

But generator's ones cannot be differentiated.

generator/lib/index.js

Lines 820 to 830 in 3d8374b

	options = _.extend(
	{
	skipInstall: this.options.skipInstall || this.options['skip-install'],
	'skip-install': this.options.skipInstall || this.options['skip-install'],
	skipCache: this.options.skipCache || this.options['skip-cache'],
	'skip-cache': this.options.skipCache || this.options['skip-cache'],
	forceInstall: this.options.forceInstall || this.options['force-install'],
	'force-install': this.options.forceInstall || this.options['force-install']
	},
	options
	);

At last and most important is that the options passed at the second parameter should not be changed for backward compatibility
We are not breaking backward compatibility for this feature.
Ex: this.options.namespace is used in a lot of places, this.options.env is used since at least generator 1.0.0.

So its needed to subtract environment options from the received options.
A workaround is:

const userOptions = {...this.options};
delete userOptions.env;
delete userOptions.resolved;
delete userOptions.namespace;
Object.keys(this.env.sharedOptions).forEach(key => delete userOptions[key]);
['skipInstall', 'skip-install', 'skipCache', 'skip-cache', 'forceInstall', 'force-install'].forEach(key => delete userOptions[key]);