Add WordPressKit unit tests

[crazytonyli]

Note

This PR depends on #24771 and will be merged after it.

Description

The first couple of commits copy the Test code from the WordPressKit repo without any changes. There are small changes to them in later commits.

Testing instructions

[dangermattic]

	2 Warnings
⚠️	Modules/Package.swift was changed without updating its corresponding Package.resolved. Please resolve the Swift packages as appropriate to your project setup (e.g. in Xcode or by running swift package resolve).
⚠️	This PR is larger than 500 lines of changes. Please consider splitting it into smaller PRs for easier and faster reviews.

Generated by 🚫 Danger

[crazytonyli]

I added the new test target to the existing test plan file. I guess Xcode did not care about the order of the target which made the diff pretty difficult to review.

[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	28699
	Version	PR #24776
	Bundle ID	org.wordpress.alpha
	Commit	cffdcaf
	Installation URL	0rt9hhg7raffg

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

[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	28699
	Version	PR #24776
	Bundle ID	com.jetpack.alpha
	Commit	cffdcaf
	Installation URL	5jcv4g9itad20

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

[wpmobilebot]

Version 26.2 has now entered code-freeze, so the milestone of this PR has been updated to 26.3.

[sonarqubecloud]

Quality Gate failed

Failed conditions
5 Security Hotspots

See analysis details on SonarQube Cloud