Apex: add NeverAllowRule for updatable

to enforce that apexes that set updatable: true also set min_sdk_version

Bug: 152655956
Test: m
Change-Id: I0d2e9f9b3234873de073ab82d91211faedd16498
diff --git a/apex/apex.go b/apex/apex.go
index 8e3e562..3f790dc 100644
--- a/apex/apex.go
+++ b/apex/apex.go
@@ -1005,6 +1005,12 @@
 }
 
 func init() {
+	android.AddNeverAllowRules(android.NeverAllow().
+		ModuleType("apex").
+		With("updatable", "true").
+		With("min_sdk_version", "").
+		Because("All updatable apexes should set min_sdk_version."))
+
 	android.RegisterModuleType("apex", BundleFactory)
 	android.RegisterModuleType("apex_test", testApexBundleFactory)
 	android.RegisterModuleType("apex_vndk", vndkApexBundleFactory)