Enforce updatable=true on apps of updatable apexes

- Update apex_info (a topdown mutator) so that it sets updatable=true on
  apps of updatable apexes
- Write a unit test that tests different combinations of
  updatable/non-updatable apks-in-apexes
- Update an existing unit test that asserts a different error

Test: go test ./java
Test: m nothing (in internal)
Bug: 209409604

Change-Id: Ie8881b857afcec44addf27fc360c5b8abf726bd2
Merged-In: Ie8881b857afcec44addf27fc360c5b8abf726bd2
(cherry picked from commit 42e89508eeb7d24bac5eb71b48aa89fbf5ed8aee)
diff --git a/java/app.go b/java/app.go
index ce58cb4..c31f9fe 100755
--- a/java/app.go
+++ b/java/app.go
@@ -847,6 +847,10 @@
 	return Bool(a.appProperties.Updatable)
 }
 
+func (a *AndroidApp) SetUpdatable(val bool) {
+	a.appProperties.Updatable = &val
+}
+
 func (a *AndroidApp) getCertString(ctx android.BaseModuleContext) string {
 	certificate, overridden := ctx.DeviceConfig().OverrideCertificateFor(ctx.ModuleName())
 	if overridden {