Improve startup performance

[cpojer]

Let's use the inline-requires and inline-imports transform (cc @zertosh do we have a combined transform yet? Otherwise, where are the two separate ones?).

How to measure:

• Measure the time it takes to run the first piece of Jest ("runJest") and bring that down.
• Measure the time it takes for the first "RUNS" to show up on a warm cache.

More startup performance wins:

• What else shall we do?

[thymikee]

• drop auto-inclusion of babel-polyfill (Drop auto-inclusion of babel-polyfill #2693)

[zertosh]

@cpojer, just inline-imports, no plans to support require. As much I... disapprove... of non-spec'ed behavior, import/export is what we use, so I can't justify the time expense into building it out for require.

[cpojer]

Also, @zertosh has a handy script here: https://gist.github.com/zertosh/1486c709fa7683c7bf1e165f114d2875

[thymikee]

We landed inline imports in Jest 21 and as a result startup is faster by ~50%
https://twitter.com/fbjest/status/904729285281423360

[github-actions]

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