UnitTestFrameworkPkg: Add googletest submodule and GoogleTestLib

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=4134

Add submodule for googletest and add GoogleTestLib that is
required for GoogleTest based unit tests. Add GoogleTest
documentation to Readme.md along with a port of the sample
unit test to the GoogleTest style.

A few typos in Readme.md are also fixed.

Cc: Michael Kubacki <mikuback@linux.microsoft.com>
Cc: Sean Brogan <sean.brogan@microsoft.com>
Cc: Andrew Fish <afish@apple.com>
Cc: Leif Lindholm <quic_llindhol@quicinc.com>
Signed-off-by: Michael D Kinney <michael.d.kinney@intel.com>
Reviewed-by: Michael Kubacki <mikuback@linux.microsoft.com>
Acked-by: Leif Lindholm <quic_llindhol@quicinc.com>

UnitTestFrameworkPkg/Library/GoogleTestLib/GoogleTestLib.inf

@@ -0,0 +1,36 @@
+## @file
+#  This module provides GoogleTest Library implementation.
+#
+#  Copyright (c) 2022, Intel Corporation. All rights reserved.<BR>
+#  SPDX-License-Identifier: BSD-2-Clause-Patent
+#
+##
+
+[Defines]
+  INF_VERSION     = 0x00010005
+  BASE_NAME       = GoogleTestLib
+  MODULE_UNI_FILE = GoogleTestLib.uni
+  FILE_GUID       = A90E4751-AD30-43CC-980B-01E356B49ADF
+  MODULE_TYPE     = BASE
+  VERSION_STRING  = 0.1
+  LIBRARY_CLASS   = GoogleTestLib|HOST_APPLICATION
+
+#
+#  VALID_ARCHITECTURES           = IA32 X64 ARM AARCH64
+#
+
+[Sources]
+  googletest/googletest/src/gtest-all.cc
+
+[Packages]
+  UnitTestFrameworkPkg/UnitTestFrameworkPkg.dec
+
+[BuildOptions]
+  MSFT:*_*_*_CC_FLAGS     == /c /EHsc /Zi
+  MSFT:NOOPT_*_*_CC_FLAGS =  /Od
+
+  GCC:*_*_*_CC_FLAGS     == -g -c
+
+  GCC:NOOPT_*_*_CC_FLAGS =  -O0
+  GCC:*_*_IA32_CC_FLAGS  =  -m32
+  GCC:*_*_X64_CC_FLAGS   =  -m64