Refactor the existing places and tests in Impress code (sd) to
use it instead.
Also keep the old property of construction and view of the theme
with a sequence of property values, but under the new property
named "ThemeUnoRepresentation". This is needed by the UI tests
currently.
Change-Id: I484567f4a603f1a5e2e03955fdd2b63132dcc66e
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/146225
Tested-by: Jenkins
Reviewed-by: Tomaž Vajngerl <quikee@gmail.com>
