feat(@schematics/angular): add --standalone to ng generate

[crisbeto]

Adds the --standalone flag when generating components, directives or pipes through ng generate.

[alfaproject]

Isn't this a duplicate of #23024

[crisbeto]

I picked this up from Alex.

[clydin]

Is standalone component generation something we want to track with analytics? If so 15 appears to be the only free slot currently.
/cc @mgechev

[crisbeto]

I've addressed the feedback.

[clydin]

Code LGTM.
Just need @mgechev & @dgp1130 approval for the analytics.

[dgp1130]

LGTM. @clydin, was slot 15 used for something else previously? I'm just wondering if there's existing data for this flag? I think I remember that we have a limited number of dimensions we can use, is that this value?

[clydin]

From the doc (https://github.com/angular/angular-cli/blob/master/docs/design/analytics.md#list-of-all-dimensions), it appears that there are only 20 allowed and number 15 was the only unused value.

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