Kernel: Implement basic shared memory objects

These can allocate memory that can be shared between processes using
a global key. There is currenly no safety checks meaning anyone can
map any shared memory object just by trying to map every possible key.

kernel/CMakeLists.txt

@@ -57,6 +57,7 @@ set(KERNEL_SOURCES
 	kernel/Memory/MemoryBackedRegion.cpp
 	kernel/Memory/MemoryRegion.cpp
 	kernel/Memory/PhysicalRange.cpp
+	kernel/Memory/SharedMemoryObject.cpp
 	kernel/Memory/VirtualRange.cpp
 	kernel/Networking/ARPTable.cpp
 	kernel/Networking/E1000/E1000.cpp