Allow Atomics methods on ArrayBuffers

[rwaldron]

I will follow up on tc39/ecma262#1908

• Atomics.notify changed to always return 0 on non-shared
• Allow non-shared array buffer:
  • Atomics.load
  • Atomics.store
  • Atomics.add
  • Atomics.sub
  • Atomics.and
  • Atomics.or
  • Atomics.xor
  • Atomics.exchange
  • Atomics.compareExchange