Rename `sourcefile` and `sourceline` to `file` and `line`

The resource endpoint was using the terms `sourceline` and
`sourcefile` to reference the manifests; other places in
the API were simply referring to these as `line` and `file`.

This commit changes the names to be consistent (`line`, `file`)
for v3, while ensuring that the old names still work properly
on the older versions of the query API.