Show the share CTA in product form navigation bar

[jaclync]

Closes: #9788

Why

Right now the share product CTA is buried inside the ellipsis menu. We can show it beside the ellipsis menu in the product form, and then hide it when there is more than one button like when the Save/Update CTA is shown after the merchant makes some changes.

How

I decided to show the share CTA on the leading edge of the existing CTA in the navigation bar, because the more/ellipsis menu can stay the same while the share CTA changes to Save/Update CTA after some unsaved changes.

The share CTA is added to ProductFormViewModel.actionButtons when there is up to 1 existing action and the product can be shared. In ProductFormViewController, the share CTA is then shown in the navigation bar that calls the same share function as from the more menu. A new event property source:product_form|more_menu was added to product_detail_share_button_tapped to see which source is the most effective.

Testing instructions

• Log in if needed
• Go to the products tab
• Tap on the + button in the navigation bar to create a product --> in the product form, there should not be a share CTA
• Tap Publish to publish the product --> after the product is saved remotely, a share CTA should be shown
• Tap on the share CTA --> product_detail_share_button_tapped event should be tracked with source: product_form and a share sheet should be shown
• Go back to the products tab
• Tap on a product --> a share CTA should be shown
• Tap on the more menu > Share --> product_detail_share_button_tapped event should be tracked with source: more_menu and a share sheet should be shown

Screenshots

Share CTA shown	Share CTA hidden when more than 1 action is shown

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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.

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[itsmeichigo]

LGTM 🚢