Opp: Use MediaStore to handle received file

getExternalStorageDirectory was deprecated in API level 29.
To improve user privacy, direct access to shared/external
storage devices is deprecated.
Use MediaStore to handle received file as alternative.
Now the files will be downloaded to the "Download" folder.

Bug: 149610220
Test: manual
Change-Id: If23459c0586114409e79cf9e5d0be1a4f3e2025c
Merged-In: I45b6fdb7ba7957d19ce3bf92c6c36711c8433c09