fix(dynamic-import-chunkname): Add proper webpack comment parsing

[st-sloth]

As briefly discussed in #1130, current webpack comment parsing logic (without taking styling into account) is severely flawed, reporting valid comments as errors while also allowing invalid syntax.

This PR adds

• checking for valid syntax the way webpack itself parses these comments
• support for multiple keys in these comments, both in a single comment and in several comments (see examples in docs or tests)

Styling requirements have not been relaxed by these changes.

The main topic of #1130 - allowing single quotes in strings in webpack comments - will be implemented on top of these changes once they are merged.

[st-sloth]

AppVeyor build failed

Locally tests pass.

[coveralls]

Coverage increased (+0.3%) to 97.393% when pulling 8d8c20a on st-sloth:webpack-comment into f7bd328 on benmosher:master.

[ljharb]

cc @lencioni @byteme980

[lencioni]

I investigated why we originally wrote this to enforce double quotes. It turns out that we have an internal babel plugin that only works with double quotes. When we wrote this rule, we assumed that this was webpack's behavior, so we encoded it the rule.

[byteme980]

LGTM, thank you for making these changes 🎉

[benmosher]

👍🏻