Add associated LANES const

Author: mulimoen

crates/core_simd/src/vector.rs

@@ -24,6 +24,9 @@ where
     LaneCount<LANES>: SupportedLaneCount,
     T: SimdElement,
 {
+    /// Number of lanes in this vector.
+    pub const LANES: usize = LANES;
+
     /// Get the number of lanes in this vector.
     pub const fn lanes(&self) -> usize {
         LANES