Fix source map missing path information

[jpvanhal]

Path information was lost from the source map due to path.basename() being run for each file in the source map. I'm not sure why this piece of code was there, but everything seems to be working fine after removing it.

Here's how the source map generated by npm run test-source-map looks now in Chrome developer tools:

Before:

After:

[jhnns]

Awesome! I'll check this PR and merge it asap.
Sorry for the delay 😞

[jhnns]

Looks good, thanks 👍

[jhnns]

Has been published with 2.2.3

[gartz]

thanks 👍

[makuko]

Unfortunately removing this code breaks paths when using the style-loader. Or at least the ones that were working before (only the resource itself, not @imported). How about instead of using path.basename() we use path.relative(loaderContext.context, file). That way paths are fine when style-loader is used. npm run test-source-map looks almost the same as without any rewriting. The only difference is that instead of ./test it will be /test.

@jpvanhal @jhnns What do you think?