Retire AsyncTask in StreamableAsset

- Replace DecodeBitmapAsyncTask with Executors
- Replace DecodeBitmapRegionAsyncTask with Executors
- Replace DecodeDimensionsAsyncTask with Executors

Bug: 198711500
Test: manual
Change-Id: Ib08262ec80f97ff0c5ed0b68a14cdf736c0563e7
1 file changed