[simd/v3i]: Implement more integer arithmetic instructions

[haoyu-zc]

Tested by:

make v3i -j && bin/spectest.v3i -tk test/regress/simd/simd_i64x2_arith2.bin.wast
make v3i -j && bin/spectest.v3i -tk test/regress/simd/simd_i32x4_arith2.bin.wast
make v3i -j && bin/spectest.v3i -tk test/regress/simd/simd_i16x8_arith2.bin.wast
make v3i -j && bin/spectest.v3i -tk test/regress/simd/simd_i8x16_arith2.bin.wast

[titzer]

lgtm with simplification suggestion

[titzer]

Please not that I just moved around some utilities in V3Eval, so you'll need to rebase.

[haoyu-zc]

Rebased accordingly. But I'm not sure which utilities should be modified by private since I noticed you removed some privates in your latest commit. For methods such as do_vv_v_x2, I think they should be private bc other files may not use them, right?

[titzer]

Functions at the top level of a file (not in a class or a component) are private by default.

[titzer]

Since these are outside the component, they don't need to be indented another level.

[haoyu-zc]

Oh, I got it. Didn't notice they were moved outside of the component. Pushed a new change.