Fill in the sv.source() range for a WorkspaceSymbol whose location carries only a URI
(i.e. OneOf::Right(WorkspaceLocation)). If the range is already present, or if the
document cannot be found, the symbol is returned unchanged.
workspace_symbols variant that queries FileIndex entries instead of
full ParsedDoc ASTs. Used by the backend for cross-file symbol search
when background files only retain a compact index.
Phase J — Thin wrapper over workspace_symbols_from_index that reads the
(Url, Arc<FileIndex>) list out of the salsa-memoized aggregate. The
inner walk is unchanged (fuzzy match is inherently O(total symbols)); the
win is that every handler shares the same aggregate Arc, rebuilt only on
edits, instead of each request rebuilding the list via all_indexes()
(which takes the host mutex once per file).