[Woo POS][Barcodes] Dark mode: corners and background when loading

[joshheald]

Description

Previously, the loading rows didn’t match the product rows, especially in dark mode.

This PR ensures that the rounded corners are shown, and a background shown in both modes.

The issue was that we relied on the ghost cell applying the border styles, but that was too low down the stack. We also relied on it for the background colour, which we now pass in through the configuration so it can be different for the cart and item list (which have different backgrounds themselves.)

Steps to reproduce

Testing information

In dark mode, add a product by scanning a barcode (or mashing keys ending in the enter button.)
Observe that you can see the rounded corners, and the background doesn't change in when it loads.

Also check the item list when opening a variable product or loading the next page – the loading cells should not have changed.

Screenshots

rounded.corners.and.background.in.dark.mode.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.

[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	30629
	Version	PR #15792
	Bundle ID	com.automattic.alpha.woocommerce
	Commit	ce81379
	Installation URL	3se828it64ka0

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

[staskus]

It'll be good to combine it with #15791 changes. It adds the corners but doesn't address the background color. I can deal with integrating after merging this.