[JuliaLowering] compat: Fix catch scope provenance (#61260)
Set explicit `srcref` for the `K"catch"` node in `est_to_dst` try
reconstruction. Previously, `[K"catch" ...]` inherited the parent `st`
(the EST `K"try"` node) as its source, causing the catch `scope_block`'s
`flattened_provenance` to resolve to `K"try"` rather than the catch
body. This made it impossible for external consumers to distinguish
catch scopes from try scopes using provenance alone.
---------
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
