UserspaceEmulator: Implement a proper VM allocator

This patch brings Kernel::RangeAllocator to UserspaceEmulator in a
slightly simplified form.

It supports the basic three allocation types needed by virt$mmap():
allocate_anywhere, allocate_specific, and allocate_randomized.

Porting virt$mmap() and virt$munmap() to use the allocator makes
UE work correctly once again. :^)

Userland/DevTools/UserspaceEmulator/CMakeLists.txt

@@ -2,6 +2,8 @@ set(SOURCES
     Emulator.cpp
     MallocTracer.cpp
     MmapRegion.cpp
+    Range.cpp
+    RangeAllocator.cpp
     Region.cpp
     SimpleRegion.cpp
     SoftCPU.cpp