Add CTS coverage for destination file checks for downloads

Restrict apps from downloading files to another app's private
directories.

Bug: 200813547
Test: atest DownloadManagerApi28Test
Test: atest DownloadManagerApiTest
Change-Id: I7e367ff7d1b72c61423b97295b0e2bfb8336b9bb
Merged-In: I7e367ff7d1b72c61423b97295b0e2bfb8336b9bb
(cherry picked from commit 760e6382f54b4dd1a1763c7d1ab8f05cd308631b)
2 files changed