Notify TextClassifier an app is reading the clipboard

Send TextClassifier an event when an app is reading the clipboard.
The event contains both the source package and the destination package.

Bug: 177898188

Will add an automated test on the text classifier side.

Test: Manual.
1. Copy and paste. Verify that an event is sent to textclassifier by
enable verbose logging.
2. Paste on the same app again, no event is sent.
3. Verify that no events are genereated for apps that read
   the clipboard in the background, e.g. keyboard and autofill.

Change-Id: Ide849bf5a0a56271ec8e70d47faabbc47a74332d