* Backstage view

[PWagner1]

• Implemented [Feature Request]: Backstage view #2510

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Note

Introduces an Office-style Backstage experience and integrates it with the ribbon.

• Adds KryptonBackstageView, KryptonBackstagePage, KryptonBackstageCommand, navigation list, and VisualBackstageOverlayForm; new enums BackstageItemSize and BackstageOverlayMode, and BackStageViewColorValues
• Integrates with KryptonRibbon: new events (BackstageOpening/Opened/Closing/Closed), overlay lifecycle, and File app tab click now opens Backstage (fallback to existing app menu); helpers to dismiss app menu and clear fixed state
• Extends RibbonFileAppTab with UseBackstageView, BackstageContent, and BackstageView properties
• Adds designers/editors for Backstage pages/view and typed collections
• Updates ViewLayoutRibbonTabsArea click handling and minor tooltip/formatting; test form updated to demo Backstage; changelog entry added

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