tools: implement node_mksnapshot

Implements a node_mksnapshot target that generates a snapshot blob
from a Node.js main instance's isolate, and serializes the data blob
with other additional data into a C++ file that can be embedded into
the Node.js binary.

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>