Update the simd.js

It is based on version https://github.com/johnmccutchan/ecmascript_simd/blob/14aa231d3c1021695ecee467ef35e5d61c8c669e/src/ecmascript_simd.js

Changes:
46620fd Add type check into SIMD operations.
1f29859 Fix float64x2.clamp implementation and add test case for it.
22b8ccf Use object properties instead of typed array as storage in polyfill
8941215 Changed conversion operators from SIMD.XXX.toYYY() to SIMD.YYY.fromXXX(), added 'select' operator for all types, added/updated tests
3eaaf69 Added reciprocal, reciprocalSqrt, shuffle, shuffleMix, comparison, and select operators to SIMD.float64x2
6f68238 Added SIMD.float64x2 (abs, neg, add, sub, mul, div, clamp, min, max, scale, sqrt, withX, withY, SIMD.float32x4.toFloat64x2)
Update SIMD.js code generation due to API update.
Merge pull request #2694 from huningxin/incoming

Update simd.js and code generation accordingly