MyBatis Allow any variable name on ognl expression when specify single value object as parameter object

Fixes gh-1486 (Related with #1237)

I've allowed to access a parameter object(value object) using any variable name on OGNL expression such as same with bind variable name.

In this change, it allow specify as follow:

public interface DemoMapper {
  List<String> selectNameByCategory(Integer category);
}

<mapper namespace="...">
  <select id="selectNameByCategory" resultType="string">
    SELECT name FROM products
    <if test="category != null">
      WHERE id = #{category}
    </if>
  </select>
</mapper>

NOTE: In version 3.5.0, #{category}(in bind variable) is valid but category != null(in OGNL expression) is invalid.

Comment From: jzdayz

ok thank you