[Do Not Merge] POS Aggregate model with multiple item types

[joshheald]

Description

This PR shows the addition of a Discount view to the item list, changing the items to be Views responsible for all their own functionality. Where they need access to the posModel for actions/other state, they can use the environment object to get it.

[dangermattic]

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

	1 Message
📖	This PR is still a Draft: some checks will be skipped.

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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	pr14290-a7215c0
	Version	20.9
	Bundle ID	com.automattic.alpha.woocommerce
	Commit	a7215c0
	App Center Build	WooCommerce - Prototype Builds #11417

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