[MBL-1329] Calculate total cost for each add-on

[ifosli]

📲 What

When users add multiple copies of an add-on, whether in the standard pledge flow or in the late pledge flow, multiply the line item cost for that add-on by the count.

👀 See

Jira

Before 🐛	After 🦋

✅ Acceptance criteria

• Line item cost matches multiplier
• Items with just one copy are unchanged

[amy-at-kickstarter]

LGTM. Have you double-checked ApplePay, as well? IIRC we just have one generic "rewards" line item there, we don't call out add-ons, but it'd be good to double-check.

[ifosli]

LGTM. Have you double-checked ApplePay, as well? IIRC we just have one generic "rewards" line item there, we don't call out add-ons, but it'd be good to double-check.

Good idea! Just did. Yeah, apple pay has one "Reward" item that includes the cost of all rewards (including multiple of each add-on, if relevant). So that one is already good (and unchanged)!

[amy-at-kickstarter]

LGTM. Have you double-checked ApplePay, as well? IIRC we just have one generic "rewards" line item there, we don't call out add-ons, but it'd be good to double-check.

Good idea! Just did. Yeah, apple pay has one "Reward" item that includes the cost of all rewards (including multiple of each add-on, if relevant). So that one is already good (and unchanged)!

Perfect. Maybe some day we can make ApplePay nicer, too, but might as well leave it as-it-was for now.