Option to feed real assets to resolveSource

[matanlurey]

i.e. something like

resolveSource(' ... ', withAssets: [
  new Glob(...),
]);

[matanlurey]

On second look, this looks non-necessary. The issue I was having is needing something like findType, not the fact that I couldn't resolve deps. I'll leave this open though if we decide we want to include this feature.

EDIT: Closing, this seems pretty rare to need in reality.