Fast edit/refresh cycles on emulators and devices

[sethladd]

• Measure our cycle on emulators and devices (Measure/benchmark edit/refresh cycle #2253)
• Drive the experience from the command-line tools
• Drive the experience from Atom

cc @devoncarew @johnmccutchan

[eseidelGoogle]

We have hot reload now. :)

[github-actions]

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