Add support for multi-dimensional array initialization

Add support for multi-dimensional array initialization

This extends impInitializeArrayIntrinsic to support MD arrays in addition to SD arrays. This includes support for SD arrays which are created via CORINFO_HELP_NEW_MDARR when the lower bound is not specified or known to be 0.

The generated code is similar to the code generated for the SD arrays, for example:
  call CORINFO_HELP_NEW_MDARR
  mov rdx, 0x202AB822050
  lea rcx, bword ptr [rax+32]
  vmovdqu ymm0, qword ptr [rdx]
  vmovdqu qword ptr [rcx], ymm0
  mov r8d, dword ptr [rdx+16]
  mov dword ptr [rcx+16], r8d

Commit migrated from https://github.com/dotnet/coreclr/commit/9c635bde59d979cd3359e5e12d743839481b38be