src: enable context snapshot after running per-context scripts

At build time, snapshot the context after running per-context scripts
in the main instance, and in the final build, deserialize the
context in the main instance.

This provides a ~5% in the misc/startup benchmark when the instance
is launched within a process that runs test/fixtures/semicolon.js.

PR-URL: https://github.com/nodejs/node/pull/27321
Refs: https://github.com/nodejs/node/issues/17058


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>