Support NaN conversion in Float32ToFloat16 Add NaN support to Float32ToFloat16. This follows Dawn's implementation: https://dawn-review.googlesource.com/c/dawn/+/8361 Bug: 3612 Test: angle_unittests Change-Id: I624bee2fc48c46b8a69cd38654679ac3cbd7c09f Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1678407 Commit-Queue: Jamie Madill <jmadill@chromium.org> Reviewed-by: Geoff Lang <geofflang@chromium.org> Reviewed-by: Jamie Madill <jmadill@chromium.org>