Convert integral value to enum value when printing Sql literal

[smitpatel]

In new query pipeline, we preserve convert nodes around enum in expression tree and remove them on both sides when translating to server.
The typeMapping for enum column expects an enum value for constant or parameter

• With new pipeline, we will have parameter's value to be enum so we no long need any additional code for conversion
• For constants, there is no convert node around constant in actual tree so we are left with integral value to be printed with Enum type mapping. Hence we need to convert it to actual enum value first. Afterwards, provider can print enum literal or apply appropriate conversions

[smitpatel]

This was causing a failure in Npgsql since it natively supports enum. Our code was not converting int to enum when there is no converter. No regression tests since we don't have a provider which supports enum without a converter.