fix(schematics): do not publish testing utilities to npm

[devversion]

• No longer publishes the CDK schematic testing utilities to NPM. We just re-exported them because the Angular Material schematic tests share logic with the CDK schematics. This now moves the CDK schematic testing utilities into a secondary entry-point that is just accessable for testing.

This is the error that shows up someone just runs any CDK or Material schematic

[jelbourn]

LGTM

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