Add EqualStub and NotEqualStub, based on the CodeStubAssembler, and hook
them up with TurboFan and Ignition. The stubs are a full implementation
of abstract equality for ES6 plus the current SIMD.js draft, unlike the
generic version of the CompareIC, which only implements a subset with
funky runtime fallbacks.

Drive-by-fix: Introduce some common helper methods.

R=epertoso@chromium.org
BUG=chromium:592690
LOG=n

Review URL: https://codereview.chromium.org/1795793002

Cr-Commit-Position: refs/heads/master@{#34806}