Handle SecurityException in ClipData.Item.coerceToText

Catch SecurityException and print a log warning.

The most likely reason for such SecurityException is
a drag and drop operation with a resource (such as a file)
for which the recipient app has no permissions.

Bug: 34716083
Test: Drag a file from Files app to Docs, Docs should not crash
Change-Id: Ib4ebbb01bd3ca87b221e15fac769368272ff4fc4