[llvm] [VPlan] Model FOR resume value extraction in VPlan. (PR #93396)

[Florian Hahn via llvm-commits]

fhahn wrote:

Updated based on the latest version of https://github.com/llvm/llvm-project/pull/93395, this now simply uses the `ExtractFromEnd` opcode. 

This leaves handling the live-out that's used in the scalar pre-header. To do so, it adds live-outs for the scalar loops header phis, which later get fixed up with the newly created phis for the resume values

https://github.com/llvm/llvm-project/pull/93396