Use Jest snapshots

[mohsen1]

Not sure if this is better than manually writing output.tsx files. This has the benefit of auto-updating snapshots but its harder to read

@vincentbel What you think?

[vincentbel]

@mohsen1 I think the original one are better:

• It's easier to read
• It is an ts file, I can get syntax highlighting, compile info, lint info in my editor
• I think people are take less care about snapshot file

In the previous PRs, the way I update outputx.tsx is I first check if the transform result are ok. If it is ok, I then overwrite the result to output.tsx by adding the following line to runner.ts.

fs.writeFileSync('output.tsx', result)

I think it's not that trouble. I can even recheck the result in git.

[mohsen1]

hehe, I did exactly that for the prettier PR. Maybe we can look for -u (--updateSnapshot) switch and write to results.