Optionally install fsevents module to prevent 100% CPU load on macOS (#12368)

[jsnajdr]

Add fsevents module as an optional (macOS) dependency. When this module is installed,
webpack-dev-server watches the project files without polling and doesn't consume CPU.

[samouri]

I love this idea. My one question is, how does this play with shrinkwrap? Do we need to change any of our scripts to install using --no-optional?
sources:

• shrinkwrap and optionalDependencies npm/npm#2679
• NPM 3.10.8 tries to install optional dep on unsupported platform when using npm-shrinkwrap.json npm/npm#14042

[jsnajdr]

Hmmm, I'll have to research how this interacts with npm shrinkwrap. One question to make sure I understand the problem: If we leave the PR as it is, then npm install --production will install also the fsevents module, right? But it shouldn't, because it's in fact a dev dependency. Is that the problem? Or anything else?

[gwwar]

Do we need to change any of our scripts to install using --no-optional

No updates are needed for the shrinkwrap generation, we already install using --no-optional in the script

See also #5386

[jsnajdr]

No updates are needed for the shrinkwrap generation, we already install using --no-optional in the script

@gwwar Does this mean that there are no obstacles to merging this PR? Running make shrinkwrap doesn't make any relevant changes to the npm-shrinkwrap.json file -- just minor version updates to some unrelated packages.

[samouri]

🚢 , this all LGTM!.