[cli] Third party libraries can be configured into config.json

[Brianzchen]

Closes #4534

Working list

• Added docs
• Change deps to defDeps to distinguish between the two kinds

[joshuanapoli]

@Brianzchen

How does react-native ship flow definitions?

The source files in the shipped package are all flow-typed. As far as I understand, the package.json refers to these flow-typed files. As configured by package.json, the flow-typed files will be loaded at "run time" by import/requre. There are no pure JavaScript files in the package. Also, configured by package.json, Typescript .d.ts files are loaded from the types directory.

Each of the main sources have a flow comment:

/**
 [...]
 * @format
 * @flow strict-local
 */

Evidently, the metro bundler strips the flow types.

I hope that this information is correct. It seems surprising to me.

[Brianzchen]

Thanks @joshuanapoli for that context. I've tried to make this work but while doing so made a shocking discovery...

Seeking more input from the flow team but at the moment limited by core flow itself.

Interestingly importing at the top level of a library definition file doesn't give an unresolved error but instead is more of a lint rule saying it's not good practice and still errors