Store package name instead of label in clipboard.

This stores the source package of a clip rather than the app
label (as added in a recent change). This is so that if the
device locale is changed, the label shown in the clipboard
access is correctly localised.

Bug: 180579171
Test: manual test, copy from Settings and from share sheet and observe
toast when pasting

Change-Id: Ib54ce8ae99fa714c5d767c260e0629dc000ea7d1