This way SalLayout can be created separately (and potentially reused)
outside vcl as well. Don't reformat the moved code, so git blame keeps
working.

This is a first step towards the goal of
<https://wiki.documentfoundation.org/Development/Budget2017#Text_layout_performance>,
in the context of code outside vcl.

Change-Id: I8b40313b5fa531d3b56c153cbc4b5ca3cec8f8df
Reviewed-on: https://gerrit.libreoffice.org/58851Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>
Tested-by: Jenkins