Add override_apex module type

override_apex module type is used to override existing apex module with
certain properties overridden. Currently, only the 'apps' property is
overridable.

Bug: 144338929
Test: m
Change-Id: Ic050b062093cda29ce78126cc92dd6097647f7db
diff --git a/apex/androidmk.go b/apex/androidmk.go
index 8ebf802..dd5da97 100644
--- a/apex/androidmk.go
+++ b/apex/androidmk.go
@@ -179,6 +179,7 @@
 				fmt.Fprintln(w, "LOCAL_MODULE_PATH :=", a.installDir.ToMakePath().String())
 				fmt.Fprintln(w, "LOCAL_MODULE_STEM :=", name+apexType.suffix())
 				fmt.Fprintln(w, "LOCAL_UNINSTALLABLE_MODULE :=", !a.installable())
+				fmt.Fprintln(w, "LOCAL_OVERRIDES_MODULES :=", strings.Join(a.properties.Overrides, " "))
 				if len(moduleNames) > 0 {
 					fmt.Fprintln(w, "LOCAL_REQUIRED_MODULES +=", strings.Join(moduleNames, " "))
 				}