Add StringLessThanStub, StringLessThanOrEqualStub, StringGreaterThanStub
and StringGreaterThanOrEqualStub, based on the CodeStubAssembler, and
hook them up with TurboFan (and Ignition). The stubs are currently
essentially comparable with the StringCompareStub, which is now
obsolete. We can later extend these stubs to cover more interesting
cases (i.e. two byte sequential string comparisons, etc.).

R=epertoso@chromium.org

Review URL: https://codereview.chromium.org/1765823002

Cr-Commit-Position: refs/heads/master@{#34485}