Move heap dump sharing to SHELL.

The system shouldn't be granting read URI permissions as itself. This
means that heap dumps aren't successfully shared. Moving the heap dump
sharing mechanism to SHELL, which already has the permission to dump
heaps so that dumps can be shared properly.

The ActivityManagerService changes are submitted separately.

Bug: 126885951
Bug: 135150619
Test: collect a heap dump and confirm it's successfully shared with an app
Test: do manual test on a secondary user & confirm it's not available to
other user

Change-Id: I6fad69280b5124c8ec2d3b4bef0f7dddb6a9422c