[clang] [llvm] [HLSL] Reapply Move length support out of the DirectX Backend (#121611) (PR #122337)

[Farzon Lotfi via llvm-commits]

farzonl wrote:

Ok going to try to merge again. no more test failure for length.hlsl in buildkite. only failing test was: `Clang.SemaSYCL/sycl-kernel-entry-point-attr-appertainment.cpp`

https://github.com/llvm/llvm-project/pull/122337