Add a webpack directive for naming icon chunks

[pugnascotia]

This PR adds a webpack directive (i.e. a comment) for naming icon chunks. The effect of this is obesrved in applications that use EUI and bundle through Webpack - instead of icon chunks such as e.g.

233.longhashgoeshereomgitssolong.js

you get:

icon.app-kibana-js.longhashgoeshereomgitssolong.js

It's a small thing, but if a dynamic download were to fail then it might make tracking down the problem fractionally easier.

I think it still works if you drop the file extension from the import(), which means you get a cleaner [request] value, but I thought I'd ask about that rather than just doing, since the .js assets live alongside the .svg assets.

[thompsongl]

Removing .js from the request was fine for dev/docs build, but resulted in module parse failures on a full build (attempting to parse the svg files).

[thompsongl]

I'm good with the changes, keeping the js extension as part of the request.

Wondering about the diff to src-docs/src/i18ntokens.json, though. Is it because comments are preserved now? Not sure what impact (if any) this has on the token changelog

[pugnascotia]

I don't know what the role of src-docs/src/i18ntokens.json is - can you or @chandlerprall comment?

[pugnascotia]

nudging @chandlerprall

[chandlerprall]

I think it still works if you drop the file extension from the import(), which means you get a cleaner [request] value, but I thought I'd ask about that rather than just doing, since the .js assets live alongside the .svg assets.

The .js extension also limits how/where Webpack looks to process the dynamic import. If we don't limit to js then webpack will [pre]process the svg files as well, which is undesired.

Wondering about the diff to src-docs/src/i18ntokens.json, though. Is it because comments are preserved now? Not sure what impact (if any) this has on the token changelog

No impact (and this is a conflict in the PR, master already has those new values, this PR didn't introduce them). The lines are used only in the docs https://elastic.github.io/eui/#/package/i18n-tokens

[chandlerprall]

btw I love this change

[thompsongl]

Changing to approval after @chandlerprall input.

Just make sure the CL entry goes to master after resolving conflicts