The directionality of the text.
This is also used to disambiguate how to render bidirectional text. For example, if the text is an English phrase followed by a Hebrew phrase, in a TextDirection.ltr context the English phrase will be on the left and the Hebrew phrase to its right, while in a TextDirection.rtl context, the English phrase will be on the right and the Hebrew phrase on its left.
Defaults to the ambient Directionality, if any.
final TextDirection? textDirection;