Add support for require.resolve

[vikr01]

Closes #585

Related to discussion in #1035 (link to comment).

So far I've only added require.resolve for commonjs with no-unresolved, let me know if I should add it anywhere else.

[coveralls]

Coverage increased (+0.09%) to 97.349% when pulling 497ead0 on vikr01:feature/require-resolve into b4a2f11 on benmosher:master.

[ljharb]

This is a breaking change, however, unless it’s under an option. Can we make that change?

[vikr01]

@ljharb was thinking the same thing, yeah I'll make a version using an option

[vikr01]

Closing in favor of #1217

[ljharb]

I'm going to keep the two in sync; orphaned PRs clutter the log.

[benmosher]

@ljharb why is this a breaking change if require.resolve is part of CommonJS?

feels semver minor to me, in that it is sortof a bugfix, but broad enough that it qualifies as an added feature.

I'd prefer this over require-ing (pun intended) users to discover and enable this behavior.

[vikr01]

@benmosher There may be some who are using require.resolve on files generated at build time (instead of path.join/path.resolve).

[benmosher]

fair enough, I guess can just try to make the note to bump it to on-by-default in v3.

[ljharb]

@benmosher new warnings are almost always a breaking change.