Attach a map from filepath to unique IDs to the manifest

[beckjake]

Feature

The manifest should include a dict that maps filepaths to the unique IDs defined by that file.

Feature description

With the addition of archive files that can contain archive blocks, and anticipating a future with models in files as well, it would be convenient to be able to ask a manifest for all nodes defined in a file (and maybe other metadata about files, like checksums).

Who will this benefit?

Developers! It's especially relevant for incremental compilation.