Map the IsSplitAllowed text frame property to <draw:frame
loext:may-break-between-pages="...">. This is meant to be always a
direct formatting, so doesn't go to the style / autostyle.
Change-Id: I439fe372271e4b7db511b5e2150e2a3c2e0acf25
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/147499
Reviewed-by: Miklos Vajna <vmiklos@collabora.com>
Tested-by: Jenkins
