Tests: figure out why webpack resolver fails when webpack is present

[ljharb]

See d108b5d and #1986.

[rotu]

I investigated one such failure:

The captures jam (array path) test currently fails if you have webpack installed. I believe it's because the appropriate field changed to resolve.mainFields: https://github.com/webpack/docs/wiki/configuration#resolvepackagemains

I'm not exactly sure:

• what resolvers/webpack is supposed to do
• why we have createWebpack1ResolveSync, createWebpack2ResolveSync but NOT, e.g. createWebpack5ResolveSync
• why logic is based on the resolved version of enhanced-resolve and NOT that of webpack.

[ljharb]

For bullet point 1, it's to allow this plugin to understand webpack specifier aliases, which which it can't.

For bullet point 2, it's either because resolution didn't meaningfully change, or, because nobody filed an issue about it. I suspect the former. If webpack 3, 4, or 5 have different resolution needs, then we should have those variations as well.

For bullet point 3, I'm also assuming that the issue wasn't webpack version as much as it was enhanced resolve version, but these changes predate me.