Consolidate NNAPI VTS utility code

This CL does additional NNAPI VTS test cleanup, including consolidating
duplicate functionality. Specifically, this CL:
* consolidates the createPreparedModel function, removing the duplicate
* consolidates the std::out ErrorStatus and DeviceStatus code into Utils
* changes non-null constant pointers to constant references
* removes redudant leading namespace specifiers (V1_0::, ::testing, etc.)
* makes the Valdiation tests free functions
* renames device to kDevice and mTestModel to kTestModel

Bug: N/A
Test: mma
Test: VtsHalNeuralnetworksV1_*TargetTest (with sample-all)
Change-Id: Ic401bb1f1760cc10384ac0d30c0c93409b63a9c7
Merged-In: Ic401bb1f1760cc10384ac0d30c0c93409b63a9c7
(cherry picked from commit e16af0a44ba9b76667a598b10a085f808efb8c7c)
diff --git a/neuralnetworks/1.0/vts/functional/Utils.cpp b/neuralnetworks/1.0/vts/functional/Utils.cpp
index 5de99fd..307003c 100644
--- a/neuralnetworks/1.0/vts/functional/Utils.cpp
+++ b/neuralnetworks/1.0/vts/functional/Utils.cpp
@@ -26,6 +26,7 @@
 #include <hidlmemory/mapping.h>
 
 #include <algorithm>
+#include <iostream>
 #include <vector>
 
 namespace android::hardware::neuralnetworks {
@@ -117,3 +118,15 @@
 }
 
 }  // namespace android::hardware::neuralnetworks
+
+namespace android::hardware::neuralnetworks::V1_0 {
+
+::std::ostream& operator<<(::std::ostream& os, ErrorStatus errorStatus) {
+    return os << toString(errorStatus);
+}
+
+::std::ostream& operator<<(::std::ostream& os, DeviceStatus deviceStatus) {
+    return os << toString(deviceStatus);
+}
+
+}  // namespace android::hardware::neuralnetworks::V1_0