This change is the last part of enabling the W^X support. It adds the
actual executable allocator that handles all double mapped memory
allocations and creating the writeable mappings.

The platform specific functionality is placed in a new minipal that is
going to be a basis for future removal of Windows APIs usage from the
native runtime.

The last state of the change was tested on all the platforms that we
support using coreclr pri 1 tests with both the W^X enabled and disabled
using the COMPlus_EnableWXORX variable.

The debugger changes were tested using the managed debugger testing
suite on Windows x64, x86 and on Apple Silicon so far. Further testing
on other platforms is in progress.

The memfd_create was introduced in 13.0 and it is equivalent to the
shm_open(SHM_ANON, ...)

Also update the ordering list of the ExecutableAllocatorLock

Also allocate LoaderHeapFreeBlock from regular heap.