edit/createRow Default Values (#266)

Returns strings for the default value of a column when a new row is created. The values that could come back:
* `null` when there isn't a default for the column
* a string when there is a default for the column
* a placeholder (currently <TBD>) when the column cannot be updated

* Renaming EditTableMetadata to reflect its SMO source

* Implementation of returning default values

* Unit test for default values

* Reworking column defaults using default constraints

* Adding unit test for new sql script unwrapper

* Disabling flaky test

* Fixing oddities in tests, removing personal tests

* Fixing broken unit test

test/Microsoft.SqlTools.ServiceLayer.UnitTests/Utility/SqlScriptFormatterTests.cs

@@ -11,7 +11,7 @@ using Microsoft.SqlTools.ServiceLayer.QueryExecution.Contracts;
 using Microsoft.SqlTools.ServiceLayer.Utility;
 using Xunit;
 
-namespace Microsoft.SqlTools.ServiceLayer.Test.Utility
+namespace Microsoft.SqlTools.ServiceLayer.UnitTests.Utility
 {
     public class SqlScriptFormatterTests
     {
@@ -308,6 +308,20 @@ namespace Microsoft.SqlTools.ServiceLayer.Test.Utility
 
         #endregion
 
+        [Theory]
+        [InlineData("(0)", "0")]
+        [InlineData("((0))", "0")]
+        [InlineData("('')", "")]
+        [InlineData("('stuff')", "stuff")]
+        [InlineData("(N'')", "")]
+        [InlineData("(N'stuff')", "stuff")]
+        [InlineData("('''stuff')", "'stuff")]
+        [InlineData("(N'stu''''ff')", "stu''ff")]
+        public void UnescapeTest(string input, string output)
+        {
+            Assert.Equal(output, SqlScriptFormatter.UnwrapLiteral(input));
+        }
+
         private class FormatterTestDbColumn : DbColumn
         {
             public FormatterTestDbColumn(string dataType, int? precision = null, int? scale = null)