Sets whether to calculate the bidirectional base direction for the layout
according to the contents of the layout; when this flag is on (the
default), then paragraphs that begin with strong right-to-left characters
(Arabic and Hebrew principally), will have right-left-layout, paragraphs
with letters from other scripts will have left-to-right layout.
Paragraphs with only neutral characters get their direction from the
surrounding paragraphs.
When false, the choice between left-to-right and right-to-left layout is
done by according to the base direction of the Pango.Context.