I.e., don't try to create auto-layout for clipboard pages which
don't contain one; don't resize objects to text.

Also, don't invalidate items that are equal to defaults,
because explicitly set items are not the same as absent items:
pasting an object without an item makes the property to inherit
new target's default, while when the item is present, the default
doesn't apply.

Also, don't consider selected state of the page while stringifying
- this makes selected page string to differ from not-selected
clipboard page.

Change-Id: I172e03e1a8c428e5fcae3a116cc9ad8de79f1a87
Reviewed-on: https://gerrit.libreoffice.org/20871Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Andras Timar <andras.timar@collabora.com>