IVGCVSW-1964 : replace optional biases with home-grown Optional

!android-nn-driver:151788

Change-Id: Ibdc41d09b8df05e7a0360dcb8a060860dfb1bd99
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 56b0935..f0fe5a1 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -152,6 +152,7 @@
     include/armnn/IRuntime.hpp
     include/armnn/ILayerSupport.hpp
     include/armnn/INetwork.hpp
+    include/armnn/Optional.hpp
     include/armnn/Tensor.hpp
     include/armnn/TensorFwd.hpp
     include/armnn/Types.hpp
@@ -376,6 +377,7 @@
         src/armnn/test/GraphUtils.hpp
         src/armnn/test/InstrumentTests.cpp
         src/armnn/test/ObservableTest.cpp
+        src/armnn/test/OptionalTest.cpp
         src/backends/test/IsLayerSupportedTest.cpp
         src/backends/test/IsLayerSupportedTestImpl.hpp
         src/backends/test/Reference.cpp