MdePkg: Add gmock examples

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=4389

Cc: Michael D Kinney <michael.d.kinney@intel.com>
Cc: Liming Gao <gaoliming@byosoft.com.cn>
Cc: Zhiguang Liu <zhiguang.liu@intel.com>
Signed-off-by: Chris Johnson <chris.n.johnson@intel.com>
Acked-by: Liming Gao <gaoliming@byosoft.com.cn>
Reviewed-by: Oliver Smith-Denny <osde@linux.microsoft.com>
Reviewed-by: Michael D Kinney <michael.d.kinney@intel.com>

MdePkg/Test/Mock/Library/GoogleTest/MockUefiLib/MockUefiLib.cpp

@@ -0,0 +1,12 @@
+/** @file
+  Google Test mocks for UefiLib
+
+  Copyright (c) 2022, Intel Corporation. All rights reserved.
+  SPDX-License-Identifier: BSD-2-Clause-Patent
+**/
+#include <GoogleTest/Library/MockUefiLib.h>
+
+MOCK_INTERFACE_DEFINITION(MockUefiLib);
+
+MOCK_FUNCTION_DEFINITION(MockUefiLib, GetVariable2, 4, EFIAPI);
+MOCK_FUNCTION_DEFINITION(MockUefiLib, GetEfiGlobalVariable2, 3, EFIAPI);