WI01073344 - .NET 10 fixing - Group 12A - DataGrid selection state fix

[Rick-Xu-WTG]

Summary

Fix DataGrid row selection state loss during row recreation in .NET 10.

Problem

When upgrading from .NET 8 to .NET 10, DataGrid's internal row recreation cycle destroys row objects, causing all selection state to be lost. This breaks 10+ tests in CargoWise1 PR #50917 (Group 12A).

Root Cause

.NET 10 triggers SetDataGridRows() which calls ResetUIState() → clears row-level selection → rows get recreated as new objects. The old selection state is destroyed with the old row objects.

Fix

Added HashSet<int> _selectedRowCache field that maintains selection state independently of DataGrid's internal row arrays:

• Select(row): stores row index in cache
• IsSelected(row): falls back to cache when row array is empty/mismatched
• UnSelect(row): removes from cache
• ResetSelection(): intentionally does NOT clear cache (survives row recreation)
• SetDataGridRows(): re-applies cached selections to new row objects after recreation

Testing

• 10/10 net10.0 framework tests pass ✅
• 9/10 Winzor framework tests pass ✅ (1 failure is unrelated MenuItem lifecycle issue)

Changed File

• src/System.Windows.Forms/System/Windows/Forms/Controls/Unsupported/DataGrid/DataGrid.cs