This is a more appropriate name now that it does more stuff than allocate virtual memory.
To be fair, the name was a bit awkward anyway. Should have been UserVMAllocator I guess.
This can cover the entire address space at once in a more memory-efficient way.
Stress-tested using 'base64 /bin/ls' which allocates enough contiguous
virtual memory to store the entirety of /bin/ls :)
A couple of bugs and fixes later, here we are!