Conditionally restrict "New shipment" option

[RafaelKayumov]

Addresses part of WOOMOB-338

Description

When creating a new shipment by selecting all items, it results in an issue where a N+1 shipment gets created according to notice. This pr addresses the issue by restricting the "New shipment" option appearing in case if all items of the current shipment are selected.

Steps to reproduce

• Log in to a test store with WooShipping set up.
• Open a completed order with more than one physical item of different quantities.
• Tap Create shipping label > Split shipments > move items into separate shipments
• Open the newly created shipment tab.
• Select all items.
• Tap on "Move to" -> "New shipment"
• The info toast will appear saying that items were moved to shipment N+1.

Testing information

• Follow the testing steps until all items selection.
• Tap on "Move to"
• Make sure that the "New shipment" option doesn't appear.
• Deselect one of items to make the selection incomplete.
• Tap on "Move to" again.
• The "New shipment" option should now be available.

Screenshots

Before	After

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• 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.

[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	29448
	Version	PR #15532
	Bundle ID	com.automattic.alpha.woocommerce
	Commit	b25693a
	Installation URL	03312tjhp2va8

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

[itsmeichigo]

Confirmed the fix on simulator iPhone 16 Pro iOS 18.2. Code changes look good to me