Update logic for drag-and-drop URI permissions for editable TextViews

Previously, Editor.onDrop used a try/finally block to request and
release URI permissions. This doesn't work for the case when an app
sets an OnReceiveContentListener (or subclasses TextView and overrides
the onReceiveContent() method). If using a background thread to
process the content in the custom impl for receiving content,
permissions will be revoked in the finally block before the app has
had a chance to process the URI.

With this change, when Editor requests permissions, they will be bound
to the app process and released automatically when the app process
terminates.

Bug: 181178998
Test: atest CtsWindowManagerDeviceTestCases:CrossAppDragAndDropTests
Test: Manually verified using development/samples/ReceiveContentDemo
Change-Id: I7ae38069fb741925211b42c7ff28784eb9722ce3