Add SIMD

[tolauwae]

Add WebAssembly SIMD instructions proposal: https://github.com/WebAssembly/simd/blob/main/proposals/simd/SIMD.md

Overview of new opcodes: https://github.com/WebAssembly/simd/blob/main/proposals/simd/NewOpcodes.md

Full list of current opcodes: https://webassembly.github.io/spec/core/appendix/index-instructions.html?highlight=opcode

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Spectests that fail because of this missing proposal:

• [x] block.wast
• [ ] simd_address.wast
• [ ] simd_bit_shift.wast
• [ ] simd_bitwise.wast
• [ ] simd_boolean.wast
• [ ] simd_conversions.wast
• [ ] simd_f32x4_arith.wast
• [ ] simd_f32x4.wast
• [ ] simd_f32x4_cmp.wast
• [ ] simd_f32x4_pmin_pmax.wast
• [ ] simd_f32x4_rounding.wast
• [ ] simd_f64x2_arith.wast
• [ ] simd_f64x2.wast
• [ ] simd_f64x2_cmp.wast
• [ ] simd_f64x2_pmin_pmax.wast
• [ ] simd_f64x2_rounding.wast
• [ ] simd_i16x8_arith2.wast
• [ ] simd_i16x8_arith.wast
• [ ] simd_i16x8_cmp.wast
• [ ] simd_i16x8_extadd_pairwise_i8x16.wast
• [ ] simd_i16x8_extmul_i8x16.wast
• [ ] simd_i16x8_q15mulr_sat_s.wast
• [ ] simd_i16x8_sat_arith.wast
• [ ] simd_i32x4_arith2.wast
• [ ] simd_i32x4_arith.wast
• [ ] simd_i32x4_cmp.wast
• [ ] simd_i32x4_dot_i16x8.wast
• [ ] simd_i32x4_extadd_pairwise_i16x8.wast
• [ ] simd_i32x4_extmul_i16x8.wast
• [ ] simd_i32x4_trunc_sat_f32x4.wast
• [ ] simd_i32x4_trunc_sat_f64x2.wast
• [ ] simd_i64x2_arith2.wast
• [ ] simd_i64x2_arith.wast
• [ ] simd_i64x2_cmp.wast
• [ ] simd_i64x2_extmul_i32x4.wast
• [ ] simd_i8x16_arith2.wast
• [ ] simd_i8x16_arith.wast
• [ ] simd_i8x16_cmp.wast
• [ ] simd_i8x16_sat_arith.wast
• [ ] simd_int_to_int_extend.wast
• [ ] simd_lane.wast
• [ ] simd_load16_lane.wast
• [ ] simd_load32_lane.wast
• [ ] simd_load64_lane.wast
• [ ] simd_load8_lane.wast
• [ ] simd_load.wast
• [ ] simd_load_extend.wast
• [ ] simd_load_splat.wast
• [ ] simd_load_zero.wast
• [ ] simd_splat.wast
• [ ] simd_store16_lane.wast
• [ ] simd_store32_lane.wast
• [ ] simd_store64_lane.wast
• [ ] simd_store8_lane.wast
• [ ] simd_store.wast