detectRtlDirectionality method
Check the estimated directionality of str, return true if the piece of
text should be laid out in RTL direction. If isHtml is true, the string
is HTML or HTML-escaped.
Implementation
static bool detectRtlDirectionality(String str, {bool isHtml: false}) =>
estimateDirectionOfText(str, isHtml: isHtml) == TextDirection.RTL;