fix: nvarchar field filtering bug for non-ascii characters

[monoruz]

Description

in mssql when we want to filter non-ascii character we should use it in the format like:

select * from MyTable where name=N'سلام'

and if we use it like other ascii variables we get empty response

select * from MyTable where name='سلام'

Motivation and Context

in mssql it is impossible to query on non-ascii words

How Has This Been Tested?

I have added all test for charfield to this field also I have tested create and filter non-ascii chars

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added the changelog accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[long2ice]

Just add in 0.20.0 because which is not released yet

[long2ice]

What about NVarChar?

[long2ice]

What about NVarCharField?