Add documentation for MappingType.Hidden to exclude columns during DataGridView auto-generation

[Copilot]

This PR adds documentation about using MappingType.Hidden to exclude columns during DataGridView auto-generation, addressing a gap in the existing documentation.

Changes Made

Primary file: remove-autogenerated-columns-from-a-wf-datagridview-control.md

• Added explanation of MappingType.Hidden approach in the introduction
• Added new section "To prevent columns from being autogenerated" with C# and VB.NET code examples
• Updated "See also" section to include references to DataColumn.ColumnMapping and MappingType

Secondary file: autogenerate-columns-in-a-data-bound-wf-datagridview-control.md

• Added paragraph explaining how to exclude columns using MappingType.Hidden
• Updated "See also" section with relevant API references

Why This Matters

Previously, the documentation only covered removing or hiding columns after they were auto-generated. This enhancement documents how to prevent unwanted columns from being created in the first place by setting:

dataTable.Columns["SensitiveData"].ColumnMapping = MappingType.Hidden;

This approach is more efficient than post-generation removal and provides developers with a cleaner solution for excluding columns during the auto-generation process.

The changes follow Microsoft's documentation guidelines, use proper cross-references, and maintain consistency with existing content style and structure.

Fixes #1516.

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Internal previews

📄 File	🔗 Preview link
dotnet-desktop-guide/winforms/controls/autogenerate-columns-in-a-data-bound-wf-datagridview-control.md	dotnet-desktop-guide/winforms/controls/autogenerate-columns-in-a-data-bound-wf-datagridview-control
dotnet-desktop-guide/winforms/controls/remove-autogenerated-columns-from-a-wf-datagridview-control.md	dotnet-desktop-guide/winforms/controls/remove-autogenerated-columns-from-a-wf-datagridview-control