Use global class names for Core Data entities

[kean]

This is a prerequisite for #25377. For most classes that represent Core Entities, we simply use @objc class names to put them into the global namespace, which is a recommended practice. This PR updates the remaining classes, so they all follow the same practice.

Potential issues: collisions at runtime; unlikely since most of the code is now in Swift.
Note on migration: WordPress 158 is shipping in 26.8, so I added the change to it.

[dangermattic]

	1 Warning
⚠️	This PR is assigned to the milestone 26.8. This milestone is due in less than 4 days. Please make sure to get it merged by then or assign it to a milestone with a later deadline.

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[wpmobilebot]

📲 You can test the changes from this Pull Request in WordPress by scanning the QR code below to install the corresponding build.

	App Name	WordPress
	Configuration	Release-Alpha
	Build Number	31562
	Version	PR #25378
	Bundle ID	org.wordpress.alpha
	Commit	5f5e9e0
	Installation URL	1nqglkek26o90

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[wpmobilebot]

📲 You can test the changes from this Pull Request in Jetpack by scanning the QR code below to install the corresponding build.

	App Name	Jetpack
	Configuration	Release-Alpha
	Build Number	31562
	Version	PR #25378
	Bundle ID	com.jetpack.alpha
	Commit	5f5e9e0
	Installation URL	4dmji4idha0uo

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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

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