Refactor oemcrypto mock into stand alone reference code

Merge from Widevine repo of http://go/wvgerrit/46204
Refactor utility code - split the mock, step 1

Merge from Widevine repo of http://go/wvgerrit/46205
Move some OEMCrypto types to common header - split the mock, step 2

Merge from Widevine repo of http://go/wvgerrit/46206
Split mock into two -- step 3

Merge from Widevine repo of http://go/wvgerrit/47460
Split the mock into two -- step 3.5

The CL moves several files used by oemcrypto and cdm into a common
subdirectory, so that it may more easily be shared with partners.

The CORE_DISALLOW_COPY_AND_ASSIGN macro was moved to its own header in
the util/include directory.

This CL removes some references to the mock from other code, and puts
some constants and types, such as the definition of the keybox, into a
header in oemcrypto.

Test: tested as part of http://go/ag/4674759
bug: 76393338
Change-Id: I75b4bde7062ed8ee572c97ebc2f4da018f4be0c9

libwvdrmengine/oemcrypto/ref/src/keys.cpp

@@ -0,0 +1,10 @@
+// If you are using a baked-in certificate instead of supporting keyboxes,
+// you should have received a keys.cpp from Widevine that replaces this file.
+//
+// If you are not using a baked-in certificate, then you may ignore this file,
+// as it intentionally defines an empty key.
+
+#include "keys.h"
+
+const uint8_t kPrivateKey[] = { 0, };
+const size_t kPrivateKeySize = 0;