[Do Not Merge][Point of Sale] Single source of truth aggregate model experiment

[joshheald]

This PR is an in-progress experiment around moving to an aggregate model architecture within POS.

It is never intended to be merged, and it's not complete yet.

[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 larger than 300 lines of changes. Please consider splitting it into smaller PRs for easier and faster reviews.

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

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[wpmobilebot]

📲 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	pr14267-74f084d
	Version	20.9
	Bundle ID	com.automattic.alpha.woocommerce
	Commit	74f084d
	App Center Build	WooCommerce - Prototype Builds #11378

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