Enable Umbra to proactively track memory allocation

Umbra is the module to maintain the shadow memory mapping for application memory. Currently, Umbra does not track the memory allocation but wait for the client calling shadow memory creation routines to create shadow memory. Umbra should be able to proactively track the allocation and manage the shadow memory accordingly. The challenges to the proactively tracking is that there are not only `mmap` and `NtAllocateVirtualMemory` that allocates memory from the OS, there are other system calls.
One option is to use `DrMalloc` (xref #824).