Turbopack: analyzer improvement followups (#92834)
- defer computing the `EsmAssetReference` issue source from the `Span`. means that we have to pass less arguments around as well
- make `mangle("default export")` a "constant" and use that everywhere instead
Some snapshots changed, because the test runner had `source: None`, so now there are some duplicate module references in there because the new always-set `span` field forces it to be a new entry in the `data.references` hashmap.
