Add language slugs (System.Windows)

[gewarren]

Prep for dotnet/docs#45892.

(Hide whitespace changes.)

[dotnet-policy-service]

Tagging subscribers to this area: @dotnet/wpf-developers

[learn-build-service-prod]

Learn Build status updates of commit 70e1724:

✅ Validation status: passed

File	Status	Preview URL	Details
xml/System.Windows.Controls.Primitives/BulletDecorator.xml	✅Succeeded	View
xml/System.Windows.Controls.Primitives/ButtonBase.xml	✅Succeeded	View
xml/System.Windows.Controls.Primitives/GridViewRowPresenterBase.xml	✅Succeeded	View
xml/System.Windows.Controls.Primitives/Popup.xml	✅Succeeded	View
xml/System.Windows.Controls.Primitives/RangeBase.xml	✅Succeeded	View
xml/System.Windows.Controls.Primitives/StatusBar.xml	✅Succeeded	View
xml/System.Windows.Controls.Ribbon/Ribbon.xml	✅Succeeded	View
xml/System.Windows.Controls.Ribbon/RibbonContextualTabGroup.xml	✅Succeeded	View
xml/System.Windows.Controls.Ribbon/RibbonGroup.xml	✅Succeeded	View
xml/System.Windows.Controls.Ribbon/RibbonGroupSizeDefinition.xml	✅Succeeded	View
xml/System.Windows.Controls.Ribbon/RibbonGroupSizeDefinitionBaseCollection.xml	✅Succeeded	View
xml/System.Windows.Controls.Ribbon/RibbonQuickAccessToolBar.xml	✅Succeeded	View
xml/System.Windows.Controls.Ribbon/RibbonTab.xml	✅Succeeded	View
xml/System.Windows.Controls/AccessText.xml	✅Succeeded	View
xml/System.Windows.Controls/Calendar.xml	✅Succeeded	View
xml/System.Windows.Controls/CalendarDateRange.xml	✅Succeeded	View
xml/System.Windows.Controls/ColumnDefinition.xml	✅Succeeded	View
xml/System.Windows.Controls/ComboBox.xml	✅Succeeded	View
xml/System.Windows.Controls/ContentControl.xml	✅Succeeded	View
xml/System.Windows.Controls/ContextMenu.xml	✅Succeeded	View
xml/System.Windows.Controls/ContextMenuService.xml	✅Succeeded	View
xml/System.Windows.Controls/Control.xml	✅Succeeded	View
xml/System.Windows.Controls/ControlTemplate.xml	✅Succeeded	View
xml/System.Windows.Controls/DatePicker.xml	✅Succeeded	View
xml/System.Windows.Controls/FlowDocumentReader.xml	✅Succeeded	View

This comment lists only the first 25 files in the pull request.
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! Nice job.