Add smooth tab reorder animation during drag

[Z-a-r-a-k-i]

Summary of the Pull Request

Adds smooth tab reorder animation during same-window tab dragging. When a tab is dragged, other tabs animate to show where the tab will be inserted, similar to Chrome/Edge behavior.

References and Relevant Issues

• Related to [MEGATHREAD] Tab drag/drop/tear-out gaps #14900 (Tab drag/drop/tear-out gaps megathread)

Detailed Description of the Pull Request / Additional comments

• Implements TabReorderAnimator class that uses TranslateTransform to animate tabs
• Same-window drags: tabs shift left/right to create visual gap at insertion point
• Cross-window drags: also animates to show insertion point
• On drop: transforms snap back immediately to avoid conflicting with TabView's reorder animation
• Respects DisableAnimations global setting (checked at init and on settings reload)
• Disables TabView's built-in ItemContainerTransitions during drag to prevent conflicts

Validation Steps Performed

• Same-window tab reordering animates smoothly
• Cross-window tab drops animate correctly
• Animation respects DisableAnimations setting
• Drag leave resets animations properly
• Rapid pointer movement doesn't leave tabs stuck (storyboard conflicts resolved)
• Settings reload updates animation preference

PR Checklist

• Related to [MEGATHREAD] Tab drag/drop/tear-out gaps #14900
• Tests added/passed (manual validation - UI animation feature)
• Documentation updated (N/A - internal implementation)
• Schema updated (N/A - no new settings)

[Z-a-r-a-k-i]

@microsoft-github-policy-service agree

[DHowett]

WHOA. Do you have a video of this? It sounds great!

[DHowett]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[Z-a-r-a-k-i]

WHOA. Do you have a video of this? It sounds great!