feat(builders): implement prerender

[wagnermaciel]

The prerender builder starts the browser builder and the server builder. It then uses the server bundle to render an array of routes and writes the rendered html to
[browser builder output path(s)]/[route]/index.html.

[googlebot]

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[googlebot]

We found a Contributor License Agreement for you (the sender of this pull request), but were unable to find agreements for all the commit author(s) or Co-authors. If you authored these, maybe you used a different email address in the git commits than was used to sign the CLA (login here to double check)? If these were authored by someone else, then they will need to sign a CLA as well, and confirm that they're okay with these being contributed to Google.
In order to pass this check, please resolve this problem and then comment @googlebot I fixed it.. If the bot doesn't comment, it means it doesn't think anything has changed.

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[googlebot]

CLAs look good, thanks!

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[googlebot]

CLAs look good, thanks!

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[alan-agius4]

As discussed offline let's get this in, and follow up with a test clean up PR as suggested by @mgechev

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