Previously, language services were held in a global registry on
SourceKitLSPServer and shared across workspaces, requiring complex
lifetime tracking (isImmortal, shutdownOrphanedLanguageServices) to
decide when to tear them down. In practice, every language service
already stored workspace-specific properties (buildServerManager,
semanticIndexManagerTask), so sharing them across workspaces was never
truly safe. Giving each Workspace its own service instances simplifies
lifetime management: services are created when needed and shut down
with their workspace.
Remove LanguageService.isImmortal, the workspace parameter from
canHandle(toolchain:), and the initialize/clientInitialized protocol
requirements.