Support `ionic generate` for React

This issue is to track generator support for React.

> [ERROR] Cannot perform generate for React projects.
>
> Since you're using the React project type, this command won't work. The Ionic CLI
> doesn't know how to generate framework components for React projects.

Start at the Ionic CLI's `generate` command and reproduce the reported error in a React project. Trace how the React project type is handled, then make `ionic generate` work for React projects and verify that the command no longer reports it as unsupported.

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