Move to Shared - SqlSer.cs

[Kaur-Parminder]

This is part of Code merge for issue #1261. I have created .common.cs and moved the uncommon code to private methods.

[johnnypham]

There's not that much code remaining in the framework specific files. Why don't we just move it to the common file?

[Kaur-Parminder]

There's not that much code remaining in the framework specific files. Why don't we just move it to the common file?

@johnnypham I just removed the netfx and netcore classes and updated SqlSer.cs in common project with the three functions.

1. Both Serialize and DeSerialize functions uses If defs, added return statements in if block.
   2 .GetUdtAttribute function in netfx used Reflection to throw same exception so just kept the .NetCore one.

[DavoudEshtehari]

The SerializationHelperSql9 could be sealed: internal sealed class SerializationHelperSql9
Also, I see some minor possible improvements like unnecessary assignment and redundant member. You can find them in the error list window.

[DavoudEshtehari]

I'd suggest using Dictionary instead of Hashtable to avoid boxing and unboxing for s_types2Serializers:

• private static ConcurrentDictionary<Type, Serializer> s_types2Serializers;