Add Examples for Contextual Components with Generics

[kdagnan]

I added some examples of yielding a contextual component with generic types to the "Invokables" typescript guides.

As part of this, I broke the "Advanced Signature Techniques" section into two sections: "Union Types" and "Generic Types", and updated the existing example to focus specifically on the Union Types while the new Generic Types examples show using Generic Types in a single component or with contextual components.

This is my first contribution so please let me know if I am missing anything or something looks off.

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[gitKrystan]

Thanks for the contribution! ❤️ Just had a few small comments.