feat(node): Support executing npm package lifecycle scripts (preinstall/install/postinstall)

[nathanwhit]

Adds support for running npm package lifecycle scripts, opted into via a new --allow-scripts flag.

With this PR, when running deno cache (or DENO_FUTURE=1 deno install) you can specify the --allow-scripts=pkg1,pkg2 flag to run lifecycle scripts attached to the given packages.

Note at the moment this only works when nodeModulesDir is true (using the local resolver).

When a package with un-run lifecycle scripts is encountered, we emit a warning suggesting things may not work and to try running lifecycle scripts. Additionally, if a package script implicitly requires node-gyp and it's not found on the system, we emit a warning.

Extra things in this PR:

• Extracted out bits of task.rs into a separate module for reuse
• Added a couple fields to process.config in order to support node-gyp (it relies on a few variables being there)
• Drive by fix to downloading new npm packages to test registry

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TODO:

• validation for allow-scripts args (make sure it looks like an npm package)
• make allow-scripts matching smarter
• figure out what issues this closes

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Review notes:

• This adds a bunch of deps to our test registry due to using node-gyp, so it's pretty noisy

[dsherret]

Great! LGTM!