Feature: add form id to multi step form template

[jonwaldstein]

Potentially resolves GIVE-2091

Description

This adds the missing parity form ID #give-next-gen used by the classic form design to the multi-step form design. The reason is there are several gateways targeting the submit button using this form ID, which will result in unexpected behavior on multi-step form designs.

Although the give-next-gen ID was not intentionally supposed to be used this way, it's important to be consistent. In the future, i'd like to revisit how we are targeting the submit button and offer a suggestion for gateways.

Affects

• Multi-step enabled form designs & gateways targeting this ID (currently: paypal, blink, razorpay)

Visuals

N/A

Testing Instructions

Zip: https://github.com/impress-org/givewp/actions/runs/13124037939

Let's QA a gateway like razorpay who is targeting the submit button this way

• Setup a v3 form using 2 column layout / multi-step
• Make sure gateway goes through without any error about scrollIntoView

Pre-review Checklist

• Acceptance criteria satisfied and marked in related issue
• Relevant @unreleased tags included in DocBlocks
• Includes unit tests
• Reviewed by the designer (if follows a design)
• Self Review of code and UX completed

[JoshuaHungDinh]

Parity achieved! Although something is going on with my Razorpay credentials so I was unable to test the gateway. If you can share some credentials I'll give it another go - otherwise maybe we can ask QA to double check for us.

[rickalday]

Passed QA tests.