Add the close popup information

[bijington]

This PR also involves a restructuring to split out some Popup related bits

[learn-build-service-prod]

Learn Build status updates of commit 6d998cc:

❌ Validation status: errors

Please follow instructions here which may help to resolve issue.

File	Status	Preview URL	Details
docs/maui/views/popup/overview.md	❌Error		Details
docs/maui/views/index.md	⚠️Warning		Details
docs/maui/views/popup/popup-service.md	⚠️Warning		Details

docs/maui/views/popup/overview.md

• Line 25, Column 1: [Error: include-not-found - See documentation] Invalid include link: '../includes/xaml-usage.md'.
• Line 2, Column 8: [Warning: duplicate-titles - See documentation] Title 'Popup - .NET MAUI Community Toolkit - Community Toolkits for .NET' is duplicated in: 'maui/views/popup/overview.md(2,8), maui/views/popup/popup-service.md(2,8)'. Titles must be unique within a docset.
• Line 13, Column 86: [Warning: file-not-found - See documentation] Invalid file link: '../alerts/toast.md'.
• Line 13, Column 118: [Warning: file-not-found - See documentation] Invalid file link: '../alerts/snackbar.md'.

docs/maui/views/index.md

• Line 29, Column 3: [Warning: file-not-found - See documentation] Invalid file link: 'Popup.md'.

docs/maui/views/popup/popup-service.md

• Line 2, Column 8: [Warning: duplicate-titles - See documentation] Title 'Popup - .NET MAUI Community Toolkit - Community Toolkits for .NET' is duplicated in: 'maui/views/popup/overview.md(2,8), maui/views/popup/popup-service.md(2,8)'. Titles must be unique within a docset.
• Line 16, Column 126: [Warning: bookmark-not-found - See documentation] Cannot find bookmark '#defining-your-popup' in 'maui/views/popup/popup-service.md'.
• Line 132, Column 104: [Warning: file-not-found - See documentation] Invalid file link: './Popup.md'.

For more details, please refer to the build report.

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