Error if globs don't match any input files

We should error if a glob in the `files` array doesn't match any files.

Note we have to do this at Execution time, not Analysis time, because the input files might not exist before dependencies execute.

Also note currently we can only do this crudely: "are _any_ files matched by these input globs" because we don't have insight into which specific globs matched, because we delegate globbing to `fast-glob`.

However, a new replacement globbing library is in progress, which will allow tracing every entry to the original glob that produced it.