use vector<uint8_t> for byte[] in AIDL

In native world, byte stream is typically represented in uint8_t[]
or vector<uint8_t>. C++ backend already generates that way. This
change involves NDK backend.

Now NDK backend also uses vector<uint8_t> just like C++ backend.

By the way, to keep the published NDK APIs stable, the signatures
of helper functions are changed to uint8_t and they still use existing
APIs.

Bug: 144957764
Test: atest CtsNdkBinderTestCases
Change-Id: I03572bfcb89ca5fb06f75b9d44fbe12426758237