Add PBS rename as a validated WorkspaceEdit of physical identifier
sites on FrontendLanguageService. Identity is definition; locals and
params rename from their name span. Refuse aliases, virtual stdlib,
builtins, error labels, keywords, and collisions. Advertise
renameProvider with prepareProvider; refused cursors are LSP errors,
not empty success.
Housekeep DSC-0043 with LSN-0072.
