Tests on FP Math.abs()

Rationale:
As a "quality of implementation", rather than pure "spec compliance", we
require that Math.abs() clears the sign bit (but changes nothing else)
for all numbers, including NaN (signaling NaN may become quiet though).

These tests ensure that remains the case.

NOTE:
This is a better redo of reverted CL
https://android-review.googlesource.com/#/c/316351/

Test: test-art-host
Bug: 30758343

Change-Id: I2740f9aea19abd82335f1f000d92f1cdb469a1c3