fakeservicemanager: Add a clear() method

This clears all registered services.

Test: atest fakeservicemanager_test
Bug: 259549851
Change-Id: Ie563de3e5babc67b9cc02efa570bf669a92bf3e4
diff --git a/libs/fakeservicemanager/ServiceManager.cpp b/libs/fakeservicemanager/ServiceManager.cpp
index deba724..1109ad8 100644
--- a/libs/fakeservicemanager/ServiceManager.cpp
+++ b/libs/fakeservicemanager/ServiceManager.cpp
@@ -106,4 +106,8 @@
     std::vector<IServiceManager::ServiceDebugInfo> ret;
     return ret;
 }
+
+void ServiceManager::clear() {
+    mNameToService.clear();
+}
 }  // namespace android