annotate local paths

[Fil]

paths to local files in transpiled JavaScript modules are postfixed with a comment

For example, when building the documentation, we now have in docs/.observablehq/dist/_import/chart.95e875cf.js

path: "../_file/lib/gistemp.08e51068.csv"/* observablehq-file */,

in lieu of

path: "../_file/lib/gistemp.08e51068.csv",

The annotate.js scripts lists a few cases that can be annotated.