assert: lazy load acorn

[BridgeAR]

This makes sure acorn is only loaded in case it is necessary. This prevents acorn always being loaded on startup.

I decided to use the modules cache instead of special handling this. The loading
is only done rarely.

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• tests and/or benchmarks are included
• documentation is changed or added
• commit message follows commit guidelines

[BridgeAR]

CI https://ci.nodejs.org/job/node-test-pull-request/14118/

[ChALkeR]

Doesn't this make --trace-sync-io nag? This could be a semver-major.
Also, I am surprized to learn that assert now requires acorn (which is pretty huge).

Upd: ah, acorn was landed in #17581 which is a semver-major and didn't get into 9.x, so probably no need to label this semver-major.

I still am not very comfortable on having assert depend on acorn (and nag on --trace-sync-io) though.

[BridgeAR]

@ChALkeR this change will only load acorn once, when it is first required. After that, the module cache should be hit besides the error cache that is implemented here as well.

I am not a huge fan of using acorn either but it makes simple assert much more powerful. If there is a different way of doing this: I would love to know.

[BridgeAR]

@ChALkeR I guess your comment is not blocking this PR, right?

[BridgeAR]

Landed in 9c06770

Since the author-ready label was not removed, I guessed it was fine to land this.

[ChALkeR]

@BridgeAR My comment was not blocking this, but I am unhappy with how this upsets --trace-sync-io. Not sure how to work-around that while keeping acorn, though. It would be much better if V8 exposed its js parsing API, like SpiderMonkey does.