
Closes https://github.com/llvm/llvm-project/issues/99116 Implements `firstbitlow` by extracting common functionality from `firstbithigh` into a shared function while also fixing a bug for an edge case where `u64x3` and larger vectors will attempt to create vectors larger than the SPRIV max of 4. --------- Co-authored-by: Steven Perron <stevenperron@google.com>