Feature: Add find* to gain alignment with react-test-renderer

[k2snowman69]

It seems that react-test-renderer exports this package under react-test-renderer/shallow to support shallow rendering. However this package doesn't contain the low level "find" functions that make it easy to dive into a shallow component similar to react-test-renderer's default export.

The ask is to implement the following functions for consistency:

• testInstance.find()
• testInstance.findByType()
• testInstance.findByProps()
• testInstance.findAll()
• testInstance.findAllByType()
• testInstance.findAllByProps()

I know enzyme "provides a nicer higher-level API over the same functionality" my ask is to provide even basic low level to have alignment between shallow and deep core rendering engines.

I think we could probably just copy most of the logic for the deep renderer here and it should get us 80% of the way.

Then in the future Enzyme could update to use these lower level functions to help fuel it's higher level functions.