Although the containing shape is in the background (and thus the
normal paragraph text is still visible), the shape's text
was still painting over top of the normal paragraph text because
the textbox was set as opaque and not transparent.

Setting the textbox to sync the opacity value of its containing shape.

Change-Id: I02477e2fa7def1f13590afcaa7c6564dd79d6406
Reviewed-on: https://gerrit.libreoffice.org/39672Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Justin Luth <justin_luth@sil.org>