To facilitate sharing LoopIdiomTransform between AArch64 and RISC-V, this first patch moves AArch64LoopIdiomTransform from lib/Target/AArch64 to lib/Transforms/Vectorize and renames it to LoopIdiomVectorize. The following patch (#94082) will teach LoopIdiomVectorize how to generate VP intrinsics (in addition to the current masked vector style) in favor of RVV.