Update DownloadStorageProvider to include MediaStore.Downloads.

Bug: 120879205
Test: manual
Test: atest DownloadProviderTests
Test: atest cts/tests/app/src/android/app/cts/DownloadManagerTest.java
Test: atest MediaProviderTests
Test: atest cts/tests/tests/provider/src/android/provider/cts/MediaStore*
Change-Id: Ief04f55614d34ba3c8a094fbd1ede34d4fef930b
6 files changed