PlaceCommasBeforeNextStatement should handle correctly formatted text (#247)

- Fixed handling of PlaceCommasBeforeNextStatement so that it doesn't add whitespace unnecessarily. This ensures that repeated formats of the same text shouldn't keep adding whitespace
- Added tests covering a number of scenarios related to this

test/Microsoft.SqlTools.ServiceLayer.Test.Common/TestData/TSqlFormatter/TestFiles/CreateProcedure_CommaHandling2.sql

@@ -0,0 +1,9 @@
+
+CREATE PROCEDURE [dbo].[sp1]
+AS
+SELECT
+    c1
+    ,c2, c3
+FROM
+    [dbo].[T1]
+RETURN 0