[WinAppSDK CMake Support]: Metapackage samples and consumption model refinements

[ssparach]

Description

Please include a summary of the change and/or which issue is fixed. Please also include relevant motivation and context. List any dependencies that are required for this change.

Summary

This PR introduces improvements to the WindowsAppSDK CMake experience, focusing on simplifying consumption and aligning with the updated embedded CMake model.

Changes

Metapackage samples across deployment modes

• Adds samples for all four deployment modes.
• Enables consuming the metapackage directly via find_package, removing the need to manually reference individual components.

Refined embedded CMake model adoption

• Removes the need for explicit _Framework and _SelfContained targets.
• Introduces the WindowsAppSDKSelfContained property to control deployment behavior.

Post-build helper integration

• Consumes new WindowsAppSDK post-build helpers.
  Provides utilities such as validating AppX manifest generation was called etc.

Draft PR: dependent on upstream changes
This PR should only be merged once the dependent changes it consumes have been fully shipped.

Target Release

Please specify which release this PR should align with. e.g., 1.0, 1.1, 1.1 Preview 1.

Checklist

Note that /azp run currently isn't working for this repo.

• Samples build and run using the Visual Studio versions listed in the Windows development docs.
• Samples build and run on all supported platforms (x64, x86, ARM64) and configurations (Debug, Release).
• Samples set the minimum supported OS version to Windows 10 version 1809.
• Samples build clean with no warnings or errors.
• [For new samples]: Samples have completed the sample guidelines checklist and follow standardization/naming guidelines.
• Microsoft employees only: you can validate your changes by following the instructions here: https://www.osgwiki.com/wiki/WindowsAppSDK-Samples