[DirectX] DXIL scalarization

[python3kgae]

DXIL requires Vectors, and maybe some other things, to be scalarized - otherwise it isn't valid DXIL. We need to come up with an overall design for this.

Notes:

Note that group-shared vectors need to be lowered to arrays to maintain layout consistency and avoid affecting access coalescing - see #92153.

AC:

• Design that enumerates all the things that require scalarization
  • Vector Ops and Call Instruction Proposal
  • Data layout transformations for scalarization proposal
• Add the scalarizer pass [DirectX] Enable the Scalarizer pass in the DirectX backend #105178
• Add support for DirectX intrinsics to the scalarizer pass #107433
• Write a pass for Data layout scalarization #107920
• [DirectX backend] flatten multi-dimensional array into a one-dimensional array. #89646

[farzonl]

With the merging of #114332 This looks to be completed.