Handle non-image URIs and quick copies

Shows the "copied" UI if loading an image thumbnail fails. Also
updates the clipboard overlay lifecycle to handle copies in quick
succession better. Clips long text to 500 characters to speed
loading of long text for the preview.

Bug: 228618430
Bug: 228619169
Fix: 228618430
Fix: 228619169
Test: manual (using clipboard testing app)
Change-Id: Iee63ef55be97acdb169e2f7f1c0fba828fc22f36