Rewrite TextFormatter.StripCRLF

Uses StringBuilder and char span indexof search to reduce intermediate allocations.

The new implementation behaves slightly different compared to old implementation. In synthetic LFCR scenario it is correctly removed while the old implementation left the CR, which seems like an off-by-one error.

Terminal.Gui/Text/TextFormatter.cs

@@ -1,4 +1,5 @@
 #nullable enable
+using System.Buffers;
 using System.Diagnostics;
 
 namespace Terminal.Gui;
@@ -9,6 +10,9 @@ namespace Terminal.Gui;
 /// </summary>
 public class TextFormatter
 {
+    // Utilized in CRLF related helper methods for faster newline char index search.
+    private static readonly SearchValues<char> NewLineSearchValues = SearchValues.Create(['\r', '\n']);
+
     private Key _hotKey = new ();
     private int _hotKeyPos = -1;
     private List<string> _lines = new ();
@@ -1187,45 +1191,59 @@ public class TextFormatter
     // TODO: Move to StringExtensions?
     internal static string StripCRLF (string str, bool keepNewLine = false)
     {
-        List<Rune> runes = str.ToRuneList ();
+        StringBuilder stringBuilder = new();
 
-        for (var i = 0; i < runes.Count; i++)
+        ReadOnlySpan<char> remaining = str.AsSpan ();
+        while (remaining.Length > 0)
         {
-            switch ((char)runes [i].Value)
+            int nextLineBreakIndex = remaining.IndexOfAny (NewLineSearchValues);
+            if (nextLineBreakIndex == -1)
             {
-                case '\n':
-                    if (!keepNewLine)
-                    {
-                        runes.RemoveAt (i);
-                    }
-
-                    break;
-
-                case '\r':
-                    if (i + 1 < runes.Count && runes [i + 1].Value == '\n')
-                    {
-                        runes.RemoveAt (i);
-
-                        if (!keepNewLine)
-                        {
-                            runes.RemoveAt (i);
-                        }
-
-                        i++;
-                    }
-                    else
-                    {
-                        if (!keepNewLine)
-                        {
-                            runes.RemoveAt (i);
-                        }
-                    }
-
-                    break;
+                if (str.Length == remaining.Length)
+                {
+                    return str;
+                }
+                stringBuilder.Append (remaining);
+                break;
             }
-        }
 
-        return StringExtensions.ToString (runes);
+            ReadOnlySpan<char> slice = remaining.Slice (0, nextLineBreakIndex);
+            stringBuilder.Append (slice);
+
+            // Evaluate how many line break characters to preserve.
+            int stride;
+            char lineBreakChar = remaining [nextLineBreakIndex];
+            if (lineBreakChar == '\n')
+            {
+                stride = 1;
+                if (keepNewLine)
+                {
+                    stringBuilder.Append ('\n');
+                }
+            }
+            else // '\r'
+            {
+                bool crlf = (nextLineBreakIndex + 1) < remaining.Length && remaining [nextLineBreakIndex + 1] == '\n';
+                if (crlf)
+                {
+                    stride = 2;
+                    if (keepNewLine)
+                    {
+                        stringBuilder.Append ('\n');
+                    }
+                }
+                else
+                {
+                    stride = 1;
+                    if (keepNewLine)
+                    {
+                        stringBuilder.Append ('\r');
+                    }
+                }
+            }
+            remaining = remaining.Slice (slice.Length + stride);
+        }
+        return stringBuilder.ToString ();
     }
 
     // TODO: Move to StringExtensions?