refactor(devtools): check if signal graph is supported (#61915)

add a new devtools field in SupportedApis to check if the
getSignalGraphApi exists

PR Close #61915

devtools/projects/ng-devtools/src/lib/devtools.component.ts

@@ -66,6 +66,7 @@ export class DevToolsComponent implements OnDestroy {
     profiler: false,
     dependencyInjection: false,
     routes: false,
+    signals: false,
   });
   readonly ivy = signal<boolean | undefined>(undefined);