Add CommentStmt to astGenRepr (#7313)

* Added codeRepr and dumpCode to the macros module.

This allows those writing macros to write examples, get the code to generate the AST for that example, and then modify that code to be dynamic with the macro function.

tests/macros/tdumpastgen.nim

@@ -2,16 +2,33 @@ discard """
 msg: '''nnkStmtList.newTree(
   nnkVarSection.newTree(
     nnkIdentDefs.newTree(
-      newIdentNode(!"x"),
+      newIdentNode("x"),
       newEmptyNode(),
       nnkCall.newTree(
         nnkDotExpr.newTree(
-          newIdentNode(!"foo"),
-          newIdentNode(!"create")
+          newIdentNode("baz"),
+          newIdentNode("create")
         ),
         newLit(56)
       )
     )
+  ),
+  nnkProcDef.newTree(
+    newIdentNode("foo"),
+    newEmptyNode(),
+    newEmptyNode(),
+    nnkFormalParams.newTree(
+      newEmptyNode()
+    ),
+    newEmptyNode(),
+    newEmptyNode(),
+    nnkStmtList.newTree(
+      newCommentStmtNode("This is a docstring"),
+      nnkCommand.newTree(
+        newIdentNode("echo"),
+        newLit("bar")
+      )
+    )
   )
 )'''
 """
@@ -21,5 +38,8 @@ msg: '''nnkStmtList.newTree(
 import macros
 
 dumpAstGen:
-  var x = foo.create(56)
+  var x = baz.create(56)
 
+  proc foo() =
+    ## This is a docstring
+    echo "bar"