refactor(rest): move the security registrars' bodies into security-routes.ts (#23050 slice 6)

The bodies of RestServer#registerSecurityExplainEndpoints (GET/POST
{basePath}/security/explain, GET {basePath}/security/my-delegable-scope)
and RestServer#registerSecurityEndpoints (GET {basePath}/security/
suggested-bindings and its /:id/confirm and /:id/dismiss) move, unedited
and re-indented one level, to ONE new module. The class keeps both
private methods and their docblocks as host literals plus .call;
routeManager goes by value, kernelManager and securityServiceProvider as
getters. The imports only these bodies read move with them, each leaving
a pointer comment. The registrar list gains security-routes.ts (6 -> 7).

Move-only commit: the readers are re-pointed in the next commit.

Claude-Session: https://claude.ai/code/session_01Q9PZ5Pzqcus4woVvTZwWNU
Co-authored-by: Claude <noreply@anthropic.com>

Author: claude

packages/rest/src/rest-server-registrar-files.ts

@@ -39,6 +39,8 @@ export const REST_SERVER_REGISTRAR_FILES = [
     'sharing-routes.ts',
     // [#23050 slice 5] `registerAnalyticsEndpoints`' body.
     'analytics-routes.ts',
+    // [#23050 slice 6] `registerSecurityExplainEndpoints`' and `registerSecurityEndpoints`' bodies.
+    'security-routes.ts',
 ] as const;
 
 /** One file on {@link REST_SERVER_REGISTRAR_FILES}. */