Inline the simd128-tag

Implement the simd128-tag inlining for the new JSObject-based
SIMD128 types' layout.

TODO(ningxin): squash into patch-2

Conflicts:
	src/heap/heap.h
Fix invalid native context reference in simd128-tag

The solution is to inline the native context load.

BUG=XWALK-2255
Fix build error for check debug version

Change point
  PrintF ==> os