Add SIMD test suite and utility functions (#442)

harness/simdUtilities.js

test/built-ins/Simd/AUTHORS

test/built-ins/Simd/all_true.js

test/built-ins/Simd/any_true.js

test/built-ins/Simd/bit_conversion.js

test/built-ins/Simd/bit_preservation.js

test/built-ins/Simd/check.js

test/built-ins/Simd/constructor.js

test/built-ins/Simd/float_operators.js

test/built-ins/Simd/from.js

test/built-ins/Simd/from_bits.js

test/built-ins/Simd/loadn.js

test/built-ins/Simd/logical_operators.js

test/built-ins/Simd/negate.js

test/built-ins/Simd/not.js

test/built-ins/Simd/numerical_operators.js

test/built-ins/Simd/operators.js

test/built-ins/Simd/replace_lane.js

test/built-ins/Simd/round_trip.js

test/built-ins/Simd/saturate.js