[Woo POS] Expose item controllers for POS list views to use directly

[joshheald]

Closes: #

Description

This PR exposes the items controllers, and then switches between them in the ItemListView.

ItemList and ChildItemList (mostly) don't know what controller they're using, they have it passed in by the ItemListView as we swap between them.

Initially, in 452247f I did the switching in the dashboard view and then had one ItemListView per controller... but I actually think this is better. When we have searching for multiple item types, we might want to change the responsibilities of the ItemListView or add another intermediate view, to simplify knowing which controller we're searching... but equally, it might work fairly neatly.

Steps to reproduce

Enable the coupons and search feature flags

1. Launch the app and navigate to POS
2. Use the items list, search, and coupons to build and edit a cart
3. Add a coupon to the store
4. Refresh, and simulate errors/recovery
5. Observe that the lists work as expected

N.B. the search list is far from perfect, but it's all behind a feature flag. I'll improve it further in future PRs

Testing information

Tested on iPad Air running iOS 17.7.3, and a simulator running 18.3

Screenshots

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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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[dangermattic]

	1 Warning
⚠️	View files have been modified, but no screenshot or video is included in the pull request. Consider adding some for clarity.

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	29297
	Version	PR #15504
	Bundle ID	com.automattic.alpha.woocommerce
	Commit	6e27621
	Installation URL	4k6fgi6s79jb0

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[staskus]

Let's call selected ones selected or current, or it's easy to conflict with actual itemsController

Suggested change

	var itemListController: PointOfSaleItemsControllerProtocol {
	var selectedItemListController: PointOfSaleItemsControllerProtocol {

[joshheald]

It's probably clear enough now that the posModel only has specifically named controllers, no general itemsController – WDYT?

[staskus]

Yes 👍 then it's clear.

[staskus]

Thank you for this refactoring. Looks good. Thanks for additional improvements of extracting VM out of the view.

Tested on iOS 18 iPad simulator, tested products and variations with features flags disabled, and additionally coupons with feature flags enabled.