Adds float16 support for RNN.

Bug: 118608628
Test: NeuralNetworksTest_static
Change-Id: I9e87c27169a046e10357bba27ee9999595dd7170
Merged-In: I9e87c27169a046e10357bba27ee9999595dd7170
(cherry picked from commit a4d8eb970f9eaf5ef89c92b51cfa3a7b3d725cf8)
12 files changed