MudDatagrid: Fix grouping to work with filtered items cache.

[adameste]

Description

Fix datagrid grouping breaked by previous PR #6495.
GroupDefinitions were initialized with previous lazy-evaluated linq query and thus updated with every render.
With cache they get a list, which stays the same and groups don't update properly.
Fixed it by updating groupings after new items cache is created, added parameter to not update component state - that would cause infinite rendering loop.
Maybe a better solution involving more work is possible (pass function to GroupDefinition? possibly slower). This should work just fine.

How Has This Been Tested?

• Existing unit tests

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)

Checklist:

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

[codecov]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (465f37b) 91.46% compared to head (3bff07e) 91.47%.

Additional details and impacted files

@@           Coverage Diff           @@
##              dev    #6557   +/-   ##
=======================================
  Coverage   91.46%   91.47%           
=======================================
  Files         393      393           
  Lines       14876    14877    +1     
=======================================
+ Hits        13607    13608    +1     
  Misses       1269     1269           

Impacted Files	Coverage Δ
...MudBlazor/Components/DataGrid/MudDataGrid.razor.cs	88.36% <100.00%> (+0.02%)	⬆️

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[henon]

@ScarletKuro FYI

[henon]

@adameste Thank you very much for the quick fix.