Display a total product price with quantity in Discount view to match what is displayed in Order view

[staskus]

Closes: #11393

Description

When fixing other parts of product pricing within Order view #13305 I noticed a fairly easy solution for #11393.

Problem

If the product quantity is more than 1, then "Price after discount" is displayed for all the quantity of the product within the Order view, and for a single item within the Discount view. We should make sure the presentation is consistent.

Discount View	Order View

Solution

Use orderItem.subtotal within Discount view, which is a pre-tax pre-discount product price multiplied by the quantity. After #13305 is merged the fix will work well for both "Prices entered with tax" settings.

Steps to reproduce

Testing information

Steps to reproduce the behavior:

• Go to the orders tab
• Tap + to create an order
• Tap Add Products and select a product or variation
• Tap to expand the product card
• Increment the quantity to be larger than 1
• Tap Add discount
• Enter some non-zero amount to the text field
• Confirm the "Price after discount" field shows the total discounted price
• Tap Add --> after syncing
• Confirm "Price after discount" field shows the total discounted price in the order form, the same as in Discount view

Screenshots

Discount View	Order View

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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 by scanning the QR code below to install the corresponding build.

	App Name	WooCommerce iOS
	Build Number	pr13313-f9cd655
	Version	19.4
	Bundle ID	com.automattic.alpha.woocommerce
	Commit	f9cd655
	App Center Build	WooCommerce - Prototype Builds #9983

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[iamgabrielma]

Works well! 🚢