Keep AOT type to support AAC offload feature

To support AAC offload feature, AACExtractor needs to parse profile
and send to HAL.
Therefore, AACExtractor needs to keep AOT type into mMeta, and
then AOSP default common flow will pass AOT type to HAL.

Bug: 123041584
Test: build pass in Android Qt and verified AAC offload feature
in Android Pie

Change-Id: Ie954546835c682cd32b5885af92dc715414cd8ea