[Woo POS] Fix order sync from passing empty items for the products

[jaclync]

Part of #12998

Description

After merging #13188 and testing the WIP #13191, I realized that the order sync stopped working because the dashboard VM is still using the items: [POSItem] internal variable that isn't set anymore after extracting the item selector logic in #13188. Without the item list, order sync cannot properly set the order line items in the API request and it results in 0 order total and an empty order in core. This PR fixes it by removing the items variable and replacing its usage in order sync with itemSelectorViewModel.items.

Steps to reproduce

Prerequisite: the store is eligible for POS and the feature switch is enabled in Menu > Settings > Experimental Features > POS

• Launch app
• Go to Menu > Point of Sale
• Add an item (with a non-zero price) to cart
• Tap Checkout --> the order total should be updated to a correct, non-zero value (before this PR in trunk, the order total is always 0 after the sync)

Testing information

Screenshots

Simulator.Screen.Recording.-.iPad.10th.generation.-.2024-06-28.at.16.36.37.mp4

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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.

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

	App Name	WooCommerce iOS
	Build Number	pr13205-e0a7ed4
	Version	19.3
	Bundle ID	com.automattic.alpha.woocommerce
	Commit	e0a7ed4
	App Center Build	WooCommerce - Prototype Builds #9812

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[iamgabrielma]

Looks good, thanks for addressing this!