Tests: Add a unit test to ensure the /dev/mem device works correctly

To ensure everything works as expected, a unit test was added with
multiple scenarios.
This binary has to have the SetUID flag, and we also bind-mount the
/usr/Tests directory to allow running of SetUID binaries.

Tests/Kernel/CMakeLists.txt

@@ -37,6 +37,7 @@ set(LIBTEST_BASED_SOURCES
     TestKernelFilePermissions.cpp
     TestKernelPledge.cpp
     TestKernelUnveil.cpp
+    TestMemoryDeviceMmap.cpp
     TestMunMap.cpp
     TestProcFS.cpp
 )