updated FirebirdTests/SqlServerExpressionsTest

Fixed a typo with SqlServerExpressionsTests folder and project name:
renamed from SqlServerExpressionsTets to SqlServerExpressionsTest.

FirebirdTests updated to use the overloaded ByExample() method with
excludeNulls parameter.

SqlServerTests updated with JoinTest.cs and IgnoreFieldSelectTest.cs
copied from SqlLiteTest.