This provides a single type for handling both literal and wildcard
ignore patterns, allowing us to tighten up a few interfaces.

The most crucial piece is fixing the hasher to make its prefix checks
without the wildcard suffix for the purpose of determining whether the
ignore affects the root project; otherwise, wildcards on the root of the
current project (why would you do this?) would be erroneously included
in hash inputs.

This also adds `dep hash-inputs` output to both of the harness tests, so
that it's easier for developers to keep track of the expected output in
these cases.

It's clearer just to use the string literal in this case.