Cherry pick 18.4 changes to udc-widevine-dev

Get the udc-widevine-dev Android branch and oemcrypto-v18 cdm branch in
sync. The commit ID for 18.4 on oemcrypto-v18 is
a2f23a2281e5e06dc2867585bdc516fa132b6396.

Merged from go/wvgerrit/190151

Bug: 290252845
Test: WVTS tests are running and passing
Change-Id: I457332e7ca70a5b5169345e1279b3eb9f18413b6

libwvdrmengine/oemcrypto/util/test/oem_cert_test.h

@@ -0,0 +1,27 @@
+// Copyright 2022 Google LLC. All Rights Reserved. This file and proprietary
+// source code may only be used and distributed under the Widevine License
+// Agreement.
+//
+// This header is used to access the testing OEM certificate.
+#ifndef OEM_CERT_TEST_H_
+#define OEM_CERT_TEST_H_
+
+#include <stddef.h>
+#include <stdint.h>
+
+namespace wvoec {
+namespace util {
+
+// Refer to the following in main modules
+extern const uint32_t kOEMSystemId;
+
+extern const uint8_t* kOEMPrivateKey;
+extern const uint8_t* kOEMPublicCert;
+
+extern const size_t kOEMPrivateKeySize;
+extern const size_t kOEMPublicCertSize;
+
+}  // namespace util
+}  // namespace wvoec
+
+#endif  // OEM_CERT_TEST_H_