Libcore: Fix or suppress EqualsNaN warning in tests

The FloatTest/DoubleTest explicitly check for NaN comparison. Ignore
the errorprone warning.

Fix incorrect comparison in MathTest.

Bug: 72451126
Test: m javac-check RUN_ERROR_PRONE=true
Change-Id: I24bbfbc468162765c29f9fbfea3f20e4b2007059
3 files changed