Use ts-jest mapper helper to map tsconfig paths to jest paths

[just-jeb]

Is your feature request related to a problem? Please describe.
Today if the user is using paths in tsconfig.json he has to define the mappings manually in jest.config.js.

Describe the solution you'd like
We can save the user the headache by using this approach for mapping tsconfig paths.

[AdditionAddict]

As the one who went through this headache there's a few things to bear in mind either way (I lack the experience and knowledge to say either way):

1. You'll get an error if you implement the ts-jest helper but don't have path in tsconfig.json due to compilerOptions.paths being undefined.
2. There's still a headache of putting paths in tsconfig.json and having to repeat the custom paths in tsconfig.app.json

[arturovt]

Closing as implemented.

[arturovt]

Whoops, wrongly closed...