servicemanager: expose updatable-via-apex

Service manager is already reading VINTF, so processes that need this
information can access this information w/o needing more permissions.

Bug: 185832616
Test: two added tests + manually specifying updatable-via-apex on a
    service and checking the result
Change-Id: Id86a72d49466048a3e2173e40526981abb6f3123
diff --git a/libs/fakeservicemanager/ServiceManager.cpp b/libs/fakeservicemanager/ServiceManager.cpp
index 4ecbe53..761e45c 100644
--- a/libs/fakeservicemanager/ServiceManager.cpp
+++ b/libs/fakeservicemanager/ServiceManager.cpp
@@ -73,4 +73,9 @@
     return out;
 }
 
+std::optional<String16> ServiceManager::updatableViaApex(const String16& name) {
+    (void)name;
+    return std::nullopt;
+}
+
 }  // namespace android