Change clipboard access notification wording.

This changes the wording of the clipboard access toast
notifications to: "<App> pasted text you copied" or
"<App> pasted content you copied".

A string is also included for the case "<App> pasted an
image you copied" - a future change may add support for that
case if needed.

Bug: 179469804
Test: manual, copy text and non-text and check notification is
correct.

Change-Id: I426c38c53316362bd8e79ec2b2ff40fa420ac071