[WebAssembly] Change SIMD lane indices to vec_i8imm_op

[tlively]

Summary

To explicitly opt out of LEB encoding for these immediates.

lib/Target/WebAssembly/WebAssemblyInstrSIMD.td

SIMD_I<(outs), (ins P2Align:$align, offset32_op:$off, I32:$addr, V128:$vec),
            (outs), (ins P2Align:$align, offset32_op:$off), [],
            "v128.store\t${off}(${addr})$align, $vec",
            "v128.store\t$off$align", 2>;
 }
 multiclass ExtractLane<ValueType vec_t, string vec, ImmLeaf imm_t,
                        WebAssemblyRegClass reg_t, bits<32> simdop,
                        string suffix = "", SDNode extract = vector_extract> {
   defm EXTRACT_LANE_#vec_t#suffix :
-      SIMD_I<(outs reg_t:$dst), (ins V128:$vec, i32imm_op:$idx),
-             (outs), (ins i32imm_op:$idx),
+      SIMD_I<(outs reg_t:$dst), (ins V128:$vec, vec_i8imm_op:$idx),
+             (outs), (ins vec_i8imm_op:$idx),
              [(set reg_t:$dst, (extract (vec_t V128:$vec), (i32 imm_t:$idx)))],
              vec#".extract_lane"#suffix#"\t$dst, $vec, $idx",
              vec#".extract_lane"#suffix#"\t$idx", simdop>;
 }
 multiclass ExtractPat<ValueType lane_t, int mask> {
   def _s : PatFrag<(ops node:$vec, node:$idx),
                    (i32 (sext_inreg
                      (i32 (vector_extract
defm "" : ExtractLane<v16i8, "i8x16", LaneIdx16, I32, baseInst, sign,
                         !cast<PatFrag>("extract_i8x16"#sign)>;
   defm "" : ExtractLane<v8i16, "i16x8", LaneIdx8, I32, !add(baseInst, 2), sign,
                         !cast<PatFrag>("extract_i16x8"#sign)>;
 }
 multiclass ReplaceLane<ValueType vec_t, string vec, ImmLeaf imm_t,
                        WebAssemblyRegClass reg_t, ValueType lane_t,
                        bits<32> simdop> {
   defm REPLACE_LANE_#vec_t :
-      SIMD_I<(outs V128:$dst), (ins V128:$vec, i32imm_op:$idx, reg_t:$x),
-             (outs), (ins i32imm_op:$idx),
+      SIMD_I<(outs V128:$dst), (ins V128:$vec, vec_i8imm_op:$idx, reg_t:$x),
+             (outs), (ins vec_i8imm_op:$idx),
              [(set V128:$dst, (vector_insert
                (vec_t V128:$vec), (lane_t reg_t:$x), (i32 imm_t:$idx)))],
              vec#".replace_lane\t$dst, $vec, $idx, $x",
              vec#".replace_lane\t$idx", simdop>;
 }
 def splat2 : PatFrag<(ops node:$x), (build_vector node:$x, node:$x)>;
 def splat4 : PatFrag<(ops node:$x), (build_vector
                        node:$x, node:$x, node:$x, node:$x)>;