Update File Explorer context menu guidance

[xandfis]

Summary

• document Windows 11 context menu integration through IExplorerCommand
• describe COM and package-manifest registration for packaged and sparse-manifested apps
• remove obsolete Windows 10 file-association walkthrough and retired screenshots

Validation

• Editor diagnostics clean
• git diff --check

[prmerger-automator]

@xandfis : Thanks for your contribution! The author(s) and reviewer(s) have been notified to review your proposed change. @stevewhims

[prmerger-automator]

@xandfis : Thanks for your contribution! The author(s) and reviewer(s) have been notified to review your proposed change. @stevewhims

[learn-build-service-prod]

Learn Build status updates of commit d52663c:

✅ Validation status: passed

File	Status	Preview URL	Details
hub/apps/desktop/modernize/images/file-explorer/folder-context-menu.png	✅Succeeded	n/a (file deleted or renamed)
hub/apps/desktop/modernize/images/file-explorer/popup.png	✅Succeeded	n/a (file deleted or renamed)
hub/apps/desktop/modernize/images/file-explorer/resize-file.png	✅Succeeded	n/a (file deleted or renamed)
hub/apps/desktop/modernize/integrate-packaged-app-with-file-explorer.md	✅Succeeded

For more details, please refer to the build report.

[prmerger-automator]

PRMerger Results

Issue	Description
File Change Percent	This PR contains file(s) with more than 30% file change.