More tests for whitespace in multi-line strings (#432)

* More tests for whitespace in multi-line strings

* replace \r\n with \n in slashdash_newline_before_node.kdl

tests/test_cases/expected_kdl/multiline_string_whitespace_only.kdl

@@ -1 +1 @@
-node "" "" "\n"
+node "" "" "" "\n\n    " "\n"

tests/test_cases/expected_kdl/slashdash_newline_before_node.kdl

@@ -1 +1 @@
-
+

tests/test_cases/input/multiline_string_whitespace_only.kdl

@@ -1,12 +1,18 @@
 // This file deliberately contains unusual whitespace
-// the first two strings are empty
+// The first two strings are empty
 node """
   	""" """
  	 \
              
- 	 """ \
+ 	 """ """
-    \ // The next string contains only whitespace
+                            
+ """\
+    \ // The next two strings contains only whitespace
     """
        
+       
+      \s 
+    """ #"""
+    
 
-    """
+  """#