Add SIMD narrowing and widening instructions

[dcodeIO]

Adds the narrowing

• i8x16.narrow_i16x8_s
• i8x16.narrow_i16x8_u
• i16x8.narrow_i32x4_s
• i16x8.narrow_i32x4_u

and widening

• i16x8.widen_low_i8x16_s
• i16x8.widen_high_i8x16_s
• i16x8.widen_low_i8x16_u
• i16x8.widen_high_i8x16_u
• i32x4.widen_low_i16x8_s
• i32x4.widen_high_i16x8_s
• i32x4.widen_low_i16x8_u
• i32x4.widen_high_i16x8_u

instructions incl. their respective generic variants

• v128.narrow<T>
• v128.widen_low<T>
• v128.widen_high<T>

and renames

• v128.trunc<T> to v128.trunc_sat<T> for consistency,
• any instructions with misplaced _s_ _u_ to the respective correct one and
• internal v128 op enums to shorter names better matching the naming of other instructions.