Pass the dimensions of the region to the paintDialog call to paint only
that much of the region in the dialog.

The DIALOG_INVALIDATE callback also returns a 'rectangle' field now in
the payload that tells the region of the dialog invalidated. It can be
used in combination with the new paintDialog call then to paint only the
invalidated region in the dialog.

Change-Id: Iebb228865c71684e0f75dd01271b71ae41a0f906
Reviewed-on: https://gerrit.libreoffice.org/44472Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: pranavk <pranavk@collabora.co.uk>