[stubs] Unify (and optimize) implementation of ToObject.

[stubs] Unify (and optimize) implementation of ToObject.

This is the initial (big) step towards a more uniform implementation of
the ToObject abstract operation (ES6 7.1.13), where we have a fallback
implementation in JSReceiver::ToObject() and a fast (hydrogen) CodeStub
to deal with the fast case (we should be able to do more cleanup on this
in a followup CL).  For natives we expose the abstract operation via a
%_ToObject intrinsic, also exposed via a macro TO_OBJECT, that unifies
the previous confusion with TO_OBJECT_INLINE, ToObject, TO_OBJECT,
$toObject and %$toObject.  Now the whole implementation of the abstract
operation is context independent, meaning we don't need any magic in the
builtins object nor the native context.

R=mvstanton@chromium.org,yangguo@chromium.org

Review URL: https://codereview.chromium.org/1266013006

Cr-Commit-Position: refs/heads/master@{#29953}