[turbofan] Add new Float32Abs and Float64Abs operators.

[turbofan] Add new Float32Abs and Float64Abs operators.

These operators compute the absolute floating point value of some
arbitrary input, and are implemented without any branches (i.e. using
vabs on arm, and andps/andpd on x86).

R=svenpanne@chromium.org

Review URL: https://codereview.chromium.org/1066393002

Cr-Commit-Position: refs/heads/master@{#27662}