Add language slugs (WinForms)

[gewarren]

Prep for dotnet/docs#45892.

(Hide whitespace changes.)

[learn-build-service-prod]

Learn Build status updates of commit 51f5c7b:

✅ Validation status: passed

File	Status	Preview URL	Details
xml/System.Windows.Forms.Integration/WindowsFormsHost.xml	✅Succeeded	View
xml/System.Windows.Forms/BindingContext.xml	✅Succeeded	View
xml/System.Windows.Forms/ComboBox.xml	✅Succeeded	View
xml/System.Windows.Forms/Control.xml	✅Succeeded	View
xml/System.Windows.Forms/Cursor.xml	✅Succeeded	View
xml/System.Windows.Forms/DataGridViewCell.xml	✅Succeeded	View
xml/System.Windows.Forms/DataGridViewComboBoxColumn.xml	✅Succeeded	View
xml/System.Windows.Forms/DataGridViewRow.xml	✅Succeeded	View
xml/System.Windows.Forms/DomainUpDown.xml	✅Succeeded	View
xml/System.Windows.Forms/ToolStripMenuItem.xml	✅Succeeded	View
xml/System.Windows.Forms/TreeView.xml	✅Succeeded	View

For more details, please refer to the build report.

For any questions, please:

• Try searching the learn.microsoft.com contributor guides
• Post your question in the Learn support channel

[gewarren]

@adegeo Could you review this one?

[adegeo]

LGTM.