Test readonly request input in AIDL VTS.

This CL modifies the AIDL generated tests to use readonly memory pool
for request inputs.

Bug: 188104713
Test: VtsHalNeuralnetworksTargetTest
Change-Id: I9e62f1cdeb501bf29bcb9c56317a452c9105b272
Merged-In: I9e62f1cdeb501bf29bcb9c56317a452c9105b272
(cherry picked from commit dfc013ad)