SIMD PR3 — load/store SIMD from pointers

[paugier]

• Related to Explicit vectorization (SIMD) in SPy — design plan #653
• Depends on Add interp memory read/write for i8, u32, i64, u64, f32 and corresponding tests #654, SIMD PR1 — Core SIMD type + C codegen #656 and SIMD PR2 — arithmetic, comparison and select #657