MdePkg/Include/Library: Add UnitTestLib class

MdePkg/Include/Library: Add UnitTestLib class

https://bugzilla.tianocore.org/show_bug.cgi?id=2505

Add UnitTestLib class to MdePkg that provides services
and macros to implement unit tests.  These services and
macros support the following features:

* Create a Unit Test Framework
* Add a Unit Test Suite to a Unit Test Framework
  + Support optional step that executes before a Unit
    Test Suite is started.
  + Support optional step that executes after a Unit
    Test Suite is finished.
* Add a Unit Test to a Unit Test Suite
  + Support optional step that executes before a Unit
    Test is started.
  + Support optional step that executes after a Unit
    Test is finished.
* Run all unit tests added to a Unit Test Framework
* Save Unit Test Framework state to persistent storage
* Support assertion checks in a unit test for TRUE, FALSE,
  EQUAL, MEM_EQUAL, NOT_EFI_ERROR, STATUS_EQUAL, and NOT_NULL.
* Support generation of log messages at ERROR, WARN, INFO,
  and VERBOSE levels.

Cc: Sean Brogan <sean.brogan@microsoft.com>
Cc: Bret Barkelew <Bret.Barkelew@microsoft.com>
Cc: Liming Gao <liming.gao@intel.com>
Signed-off-by: Michael D Kinney <michael.d.kinney@intel.com>
Reviewed-by: Bret Barkelew <Bret.Barkelew@microsoft.com>
Reviewed-by: Michael D Kinney <michael.d.kinney@intel.com>
Reviewed-by: Hao A Wu <hao.a.wu@intel.com>