Merge pull request #20515 from Therzok/sliding-window

[SlidingTextWindow] Add another common case for GetText optimization

src/Compilers/CSharp/Portable/Parser/SlidingTextWindow.cs

@@ -668,6 +668,10 @@ public string GetText(int position, int length, bool intern)
                     {
                         return " ";
                     }
+                    if (_characterWindow[offset] == '\n')
+                    {
+                        return "\n";
+                    }
                     break;
 
                 case 2: