[llvm] Add LoopVectorizer support for `llvm.vector.partial.reduce.fadd` (PR #163975)

[Sander de Smalen via llvm-commits]

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sdesmalen-arm wrote:

Do we want to handle this case as well, i.e. `reduce.fadd(fpext(..))` ?

https://github.com/llvm/llvm-project/pull/163975