filter import map entries and handle relative exports from dependency entry points

[thescientist13]

Related Issue

resolves #748 and #773 to fix issues observed while integrating MWC - ProjectEvergreen/greenwood-getting-started#42

Just a quick and dirty approach that seemed to work and passed all the tests, not sure if the best, so just putting in a draft for now. Should also look at the foundation issue as well in the linked PR.

Summary of Changes

1. Filter out entries that aren't file paths
2. Handle relative export paths from dependency entry points

TODO

1. Add specs and clean up console logging
2. Little more manual testing to verify this is sufficient and validate full MWC interop

[thescientist13]

oh, this is just the same line, no need for the conditional? I think maybe it was supposed to be

if (path.extname(entryPath) !== '') {
    entryPath = `${entryPath}.js`;
}