Show extensions as namespaces in LSP

Author: Trzyipolkostkicukru

Sources/SourceKit/sourcekitd/SwiftLanguageServer.swift

@@ -517,6 +517,9 @@ extension SwiftLanguageServer {
             return .struct
           case self.values.decl_generic_type_param:
             return .typeParameter
+          case self.values.decl_extension:
+            // There are no extensions in LSP, so I return something vaguely similar
+            return .namespace
           default:
             return nil
         }