Detect FlowDirection from text content about avalonia

[Bip901]

Example:

This line is left-to-right because it starts with "T".
שלום! This line is right-to-left because it starts with "ש".
This line is left-to-right even though it contains Hebrew characters: שלום, because it starts with "T".

EDIT: Seems like GitHub messed this up too, it's only correct in the preview 😄

[Gillibald]

The bidi level of each line already indicates the strong direction. FlowDirection.DetectFromContent should be simple.

[Gillibald]

 var text = "שלום, John Dough";

 var codepointEnumerator = new CodepointEnumerator(text);

 var codepoint = Codepoint.ReplacementCodepoint;

 while (codepointEnumerator.MoveNext(out codepoint))
 {
     var flowDirection = GetFlowDirectionDirection(codepoint.BiDiClass);

     if (flowDirection != null)
     {
         break;
     }
 }
 
 return;

 static FlowDirection? GetFlowDirectionDirection(BidiClass bidiClass)
 {
     switch (bidiClass)
     {
         case BidiClass.ArabicLetter:
         case BidiClass.ArabicNumber:
         case BidiClass.RightToLeft:
         {
             return FlowDirection.RightToLeft;
         }
         case BidiClass.LeftToRight:
         {
             return FlowDirection.LeftToRight;
         }
     }

     return null;
 }