Adds validation for the TTS model.

Also moves AssetUtils to util sub-package.

Bug: 111594004
Bug: 116315300

Test: Covered by existing test:
com.example.android.nn.benchmark.NNTest#testNNAPI10Seconds[tts_float]

Change-Id: I3ca66b87c0c51b6a628409e5bbea2fb4e9a45154
Merged-In: I3ca66b87c0c51b6a628409e5bbea2fb4e9a45154
(cherry picked from commit befa18b17ae2f554e42b88bc7e0ea838178707f7)
9 files changed