Consolidate microsoft-ui-xaml-specs into main repository

[niels9001]

Fixes

N/A - repository documentation consolidation.

PR Type

• Bugfix
• Feature
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no API changes)
• Build related changes
• Documentation content changes
• Other

Description

Current Behavior

WinUI specifications are split between microsoft-ui-xaml and the separate microsoft-ui-xaml-specs repository.

New Behavior

• Imports non-duplicate specifications and assets from microsoft-ui-xaml-specs/active.
• Adds the imported NavigationView specs under specs/NavigationView; Reorganize specs into feature folders #11230 separately moves the existing NavigationView specs into that folder.
• Uses the active TeachingTip spec and excludes the older duplicate under api_review/teachingtip.
• Keeps the updated Grid syntax and NavigationView footer specs while excluding their stale duplicate drafts.
• Moves the WinUI 3 DispatcherQueue spec to specs/DispatcherQueue.
• Consolidates related specs under clearer folders including Grid, Progress, ProgressBar, ItemsRepeater, ItemsSourceView, and PersonPicture.
• Moves the archived Tab specification into specs/TabView and removes the obsolete archive structure.

Customer Impact

None. This consolidates specification documents and assets without changing product behavior or APIs.

Regression Potential

• Low risk - isolated change, limited scope
• Medium risk - touches shared components or public APIs
• High risk - architectural or breaking API change

How Has This Been Tested?

• I have performed a self-review of my own code
• I have added tests to cover my changes
• Existing tests pass locally

Imported files were checked for duplicate specifications, content fidelity, destination collisions, and valid relative image links.

Screenshots (if appropriate)

N/A