Use Folders for Authenticator

[jkmassel]

Similarly to #23736, this PR cleans up a bunch of the project file by moving WPAuthenticator inside the project directory and converting it to a folder-based hierarchy.

To test

• Ensure that CI passes and that the WPAuthenticator tests run

[dangermattic]

	3 Warnings
⚠️	View files have been modified, but no screenshot or video is included in the pull request. Consider adding some for clarity.
⚠️	This PR is larger than 500 lines of changes. Please consider splitting it into smaller PRs for easier and faster reviews.
⚠️	This PR is assigned to the milestone 25.5. The due date for this milestone has already passed. Please assign it to a milestone with a later deadline or check whether the release for this milestone has already been finished.

Generated by 🚫 Danger

[wpmobilebot]

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

	App Name	WordPress Alpha
	Configuration	Release-Alpha
	Build Number	pr23743-831c2ee
	Version	25.4.2
	Bundle ID	org.wordpress.alpha
	Commit	831c2ee
	App Center Build	WPiOS - One-Offs #10935

Automatticians: You can use our internal self-serve MC tool to give yourself access to App Center if needed.

[wpmobilebot]

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

	App Name	Jetpack Alpha
	Configuration	Release-Alpha
	Build Number	pr23743-831c2ee
	Version	25.4.2
	Bundle ID	com.jetpack.alpha
	Commit	831c2ee
	App Center Build	jetpack-installable-builds #9975

Automatticians: You can use our internal self-serve MC tool to give yourself access to App Center if needed.

[kean]

LGTM

[wpmobilebot]

Version 25.5 has now entered code-freeze, so the milestone of this PR has been updated to 25.6.

[kean]

Hey, looks like it has a few conflicts now.