Add support for /oem/overlay

Add support for runtime resource overlay (RRO) APKs in /oem/overlay.

Bug: 121033532
Test: manual (adb push apk to /oem/overlay, reboot, cmd overlay list)
Change-Id: I70b23b11831d57b3241e6057c745aa4ce9f795ef
diff --git a/libs/androidfw/AssetManager.cpp b/libs/androidfw/AssetManager.cpp
index 21609d3..4755cb8 100644
--- a/libs/androidfw/AssetManager.cpp
+++ b/libs/androidfw/AssetManager.cpp
@@ -76,6 +76,7 @@
 const char* AssetManager::PRODUCT_OVERLAY_DIR = "/product/overlay";
 const char* AssetManager::PRODUCT_SERVICES_OVERLAY_DIR = "/product_services/overlay";
 const char* AssetManager::ODM_OVERLAY_DIR = "/odm/overlay";
+const char* AssetManager::OEM_OVERLAY_DIR = "/oem/overlay";
 const char* AssetManager::OVERLAY_THEME_DIR_PROPERTY = "ro.boot.vendor.overlay.theme";
 const char* AssetManager::TARGET_PACKAGE_NAME = "android";
 const char* AssetManager::TARGET_APK_PATH = "/system/framework/framework-res.apk";