DataGrid: Remove 'Value not null' criteria for FilterDefinition

[aditya119]

Description

Fixes #8702
On MudDataGrid, when is empty or is not empty filters are applied. Filter icon does not show filled funnel.
This creates confusion whether filter was applied or not.

The hasFilter property in HeaderCell.razor.cs was returning false when filter definition did not have a value.
Since, is empty and is not empty filter definitions will never have a value so datagrid column header was showing empty funnel despite filter being applied.
The logic was updated to ignore the check for Value when checking whether column hasFilter.

How Has This Been Tested?

Visually tested.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation (fix or improvement to the website or code docs)

Checklist

• The PR is submitted to the correct branch (dev).
• My code follows the code style of this project.
• I've added relevant tests.

[ScarletKuro]

Hi. Thanks for PR.

Please, add a bUnit test to test this case.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.11%. Comparing base (28bc599) to head (ac88346).
Report is 63 commits behind head on dev.

Additional details and impacted files

@@            Coverage Diff             @@
##              dev    #8706      +/-   ##
==========================================
+ Coverage   89.82%   90.11%   +0.28%     
==========================================
  Files         412      418       +6     
  Lines       11878    12050     +172     
  Branches     2364     2365       +1     
==========================================
+ Hits        10670    10859     +189     
+ Misses        681      658      -23     
- Partials      527      533       +6     

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[aditya119]

Please, add a bUnit test to test this case.

Added test to check scenarios of filter definition with value, without value and filter not applied.

[ScarletKuro]

Added test to check scenarios of filter definition with value, without value and filter not applied.

Thanks!

[tjscience]

This one looks good. Thanks, @aditya119!