Shipping Labels: Inject shipments to split shipment view

[itsmeichigo]

Part of #15309

Description

In order to display shipments on the shipping label creation form, we need to load shipment details on this screen. Currently, shipment details are available only on the split shipment screen. This PR adds changes to support showing shipments on both screens.

Changes include:

• Update Shipment initializer to accept package items.
• Add a new property for shipments in the shipping creation view model.
• Send the shipments from the shipping creation view model to the split shipment screen.
• Update the split shipment view model to adapt with changes in Shipment.

Note: with the new changes, the split shipment entry point will always be available again. Logic for this will be updated when tabs are introduced in the creation form.

Steps to reproduce

No user-facing changes have been made. Please follow the testing steps in #15448, #15457, and test case 3 of #15463 to confirm that there's no regression on the split shipment screen.

Testing information

Tested split shipment screen functionalities on simulator iPhone 16 Pro iOS 18.2 and confirmed no regression.

Screenshots

N/A

---

• I have considered if this change warrants user-facing release notes and have added them to RELEASE-NOTES.txt if necessary.

Reviewer (or Author, in the case of optional code reviews):

Please make sure these conditions are met before approving the PR, or request changes if the PR needs improvement:

• The PR is small and has a clear, single focus, or a valid explanation is provided in the description. If needed, please request to split it into smaller PRs.
• Ensure Adequate Unit Test Coverage: The changes are reasonably covered by unit tests or an explanation is provided in the PR description.
• Manual Testing: The author listed all the tests they ran, including smoke tests when needed (e.g., for refactorings). The reviewer confirmed that the PR works as expected on all devices (phone/tablet) and no regressions are added.

[dangermattic]

	2 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 assigned to the milestone 22.1. This milestone is due in less than 2 days. Please make sure to get it merged by then or assign it to a milestone with a later deadline.

Generated by 🚫 Danger

[wpmobilebot]

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

	App Name	WooCommerce iOS Prototype
	Build Number	29145
	Version	PR #15475
	Bundle ID	com.automattic.alpha.woocommerce
	Commit	e85fabe
	Installation URL	5fi8mectnldmo

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