Enable Bluetooth sharing of downloaded files.

Change BT OPP to open the InputStreams of files to share in the
BluetoothOppLauncherActivity (or BluetoothOppHandoverReceiver
for NFC shares), while the process has grantUriPermission() on
the URI's to share.

InputStreams are saved inside the existing BluetoothOppSendFileInfo
objects, which no longer include the mDestination field because
this isn't known at the time the SendFileInfo object is now created
(before the user has chosen the destination BT device). These
objects are stored in a static ConcurrentHashMap in BluetoothOppUtility
and are removed when the file is closed (on success or failure).

If the user tries to share thousands of files in one batch, we may
not be able to open InputStreams for all of the files in the batch.
In this case, the open should fail gracefully.

Bug: 6808783
Change-Id: I3f3f86d2dc1a78a837aeb6a888f90b26434ba499