Add override_module.

This new module type replaces the inherit-package function in make by
allowing developers to override the name, the certificate, and the
manifest package name of an android_app module.

Bug: 122957760
Fixes: 123640028
Test: app_test.go + BrowserGoogle
Change-Id: Iefe447e7078b25039233221361ef95c83a29973a

Android.bp

@@ -55,6 +55,7 @@ bootstrap_go_package {
         "android/namespace.go",
         "android/neverallow.go",
         "android/onceper.go",
+        "android/override_module.go",
         "android/package_ctx.go",
         "android/paths.go",
         "android/prebuilt.go",