Make android_app.stem overridable

override_android_app can set "stem" property to set the APK name.

Bug: 193504286
Test: m (soong test)
Change-Id: I9ad66ea28bd1b030cb2c588d1f070d72e62ab1c7

java/app.go

@@ -1163,7 +1163,10 @@ func (i *OverrideAndroidApp) GenerateAndroidBuildActions(_ android.ModuleContext
 // some of its properties.
 func OverrideAndroidAppModuleFactory() android.Module {
 	m := &OverrideAndroidApp{}
-	m.AddProperties(&overridableAppProperties{})
+	m.AddProperties(
+		&OverridableDeviceProperties{},
+		&overridableAppProperties{},
+	)
 
 	android.InitAndroidMultiTargetsArchModule(m, android.DeviceSupported, android.MultilibCommon)
 	android.InitOverrideModule(m)