Port 5e9ddf6c

Original commit message:
    * New atomic code stubs for x64, ia32, arm, arm64
    * Add convenience functions JumpIfNotValidSmiValue, JumpIfUintNotValidSmiValue
      to macro-assembler-ia32 (API based on x64 macro assembler)
    * Remove runtime implementation of Atomics.load, the code stub should always be
      called instead
    * Add new test to mjsunit atomics test; check that Smi values of different
      sizes are supported when possible, else fall back to HeapNumbers

    These changes were needed to add another codestub:
    * Bump kStubMajorKeyBits from 7 to 8
    * Reduce ScriptContextFieldStub::kSlotIndexBits from 13 to 12

R=binji@chromium.org, joransiu@ca.ibm.com, jyan@ca.ibm.com, michael_dawson@ca.ibm.com, bjaideep@ca.ibm.com
BUG=v8:4614
LOG=N

Review URL: https://codereview.chromium.org/1887823002

Cr-Commit-Position: refs/heads/master@{#35462}