Grid multi-checkbox filter shows empty distinct values for nested field bindings

[yanmariomenev]

Description

When a Grid column is bound to a nested field path, such as Security.SecurityDisplay, the column renders its cell values correctly, but the built-in multi-checkbox filter popup shows an empty list.

This appears to be specific to the multi-checkbox filter distinct-value extraction. The Grid itself resolves complex field bindings correctly for rendering, but the filter does not populate values for the same field.

Steps To Reproduce

Example for testing - https://stackblitz.com/edit/angular-96xaouby-esrptgcz?file=src%2Fapp%2Fapp.component.ts

1. Bind the Grid to data containing nested objects, for example:
   { Security: { SecurityDisplay: 'Alpha' } }
2. Define a column with a nested field path:
   field="Security.SecurityDisplay"
3. Enable menu filtering and use the built-in multi-checkbox filter.
4. Open the filter menu for that column.

Workaround

Provide custom flattened data to the filter through the column filterVariant configuration, for example by mapping distinct nested values into objects keyed by the full field name.

https://stackblitz.com/edit/angular-96xaouby-36f1vdud?file=src%2Fapp%2Fapp.component.ts

Actual Behavior

The multi-checkbox filter list is empty.

Expected Behavior

The filter should show the distinct values for the nested field, such as Alpha and Beta, the same way the Grid resolves the field for cell rendering.