source gen and ir gen now use the same seq generator

StgSharp.RegularAnalysis/Abstraction/SequenceEmitter.cs

@@ -18,6 +18,28 @@ using System.Threading.Tasks;
 
 namespace StgSharp.RegularAnalysis.Abstraction
 {
+    public static class SequenceEmitterExtensions
+    {
+
+        public static SequenceEmitter<string> AppendLine(
+                                              this SequenceEmitter<string> emitter
+        )
+        {
+            return emitter is null ? null! : emitter.Append(string.Empty);
+        }
+
+        public static SequenceEmitter<string> AppendLine(
+                                              this SequenceEmitter<string> emitter,
+                                              string line
+        )
+        {
+            return emitter is null ?
+                   null! :
+                   emitter.Append(string.IsNullOrEmpty(line) ? string.Empty : line);
+        }
+
+    }
+
     public sealed class SequenceEmitter<T>
     {
 
@@ -35,6 +57,8 @@ namespace StgSharp.RegularAnalysis.Abstraction
 
         public int Count { get; private set; }
 
+        private static bool IsString { get; } = typeof(T) == typeof(string);
+
         public SequenceEmitter<T> Append(
                                   T unit
         )