SwTextBoxHelper::create(): initialize size

On import, syncProperty() takes care of this, but in case the user
interactively adds a textbox, when we need to handle the size in
create() as well.

Change-Id: I9428a682dbf70550bdfd081900e8098aeb64d38f
SwTextBoxHelper::create(): initialize position

The situation is a bit more complicated here,
drawing::XCustomShapeEngine returns the text rectangle in absolute
coordinates, but that's on the drawpage. So count the relative
coordinates, and then just adjust the position we got from the original
shape.

Change-Id: Ibfbc183e5170037c8c281d61ce802a19a7acda17
SwTextBoxHelper::syncProperty(): no need to pass the property name

Change-Id: Ic2f6ae15fd81826d2bc6f8796e33c3c93b34e240
SwTextBoxHelper: use UNO_NAME_* constants

Change-Id: Ie2ce95f46c19fa6c693619242a65bccc442a7fe7