Add ExAllocatePool2 support to usersim

[dthaler]

• Add ExAllocatePool2 support
• Make winuser cxplat_allocation_header_t be DEBUG only (fixes Optimize memory_winuser.cpp #111)
• Make cxplat_allocate use pool flags instead of the older pool type values
• Remove _cache_aligned APIs since there is a cache aligned pool flag
• Use non-executable memory allocation for usersim FWP NBL's
• Use cxplat_free with tag = 0 instead of a separate API cxplat_free_any_tag
• Fix double-free of a WDFDEVICE if the driver creates and then deletes a device object before being unloaded (this will get cleaned up even more once Support for multiple devices per usersim driver #114 is done)