Jest tests fail with RN >= 52 because transformer doesn't return transpiled text, only ast

[ds300]

from #39 (comment)

[ds300]

Not really sure what to do about this, except add babel-generator to the mix. But that'd be in the jest transformer wrapper, not in this package

[vovkasm]

Actually it almost unusable until jest will add ability to handle source maps for transformed files, because retain lines does not help with typescript. Some links:

• Fix support for sourcemaps in transforms jestjs/jest#5121
• Show sourcemap support in typescript example jestjs/jest#5116
• Document sourcemap support for transforms jestjs/jest#5113

I did experiments with various variants, and still my transformer looks almost like that from comment.