We already had hand-written optimized code for %_ToName in fullcodegen,
but the optimizing compilers always went to the runtime for %_ToName,
which is pretty bad for many of our builtins. So this CL moves the
existing native code to a ToNameStub (similar to the existing
ToStringStub), and uses the ToNameStub consistently in all compilers to
actually implement %_ToName.

Review URL: https://codereview.chromium.org/1622493002

Cr-Commit-Position: refs/heads/master@{#33460}