[runtime] Unify and fix the strict equality comparison.

[runtime] Unify and fix the strict equality comparison.

Add Object::StrictEquals to unify the implementation of strict equality
comparison in the runtime and the api (the api was already missing a
case for SIMD).  Now we (almost) have a single bottleneck for strict
equality, we just need to reduce the amount of unnecessary complexity
for the code stub.

R=yangguo@chromium.org

Review URL: https://codereview.chromium.org/1298603002

Cr-Commit-Position: refs/heads/master@{#30186}