Return UUIDs from addLineItem and addCustomSale

[vctrchu]

Part of https://github.com/Shopify/pos-next-react-native/issues/47964

Background

Updates the addLineItem and addCustomSale interfaces to return UUID strings or undefined when promises complete.

[vctrchu]

/snapit

[shopify-github-actions-access]

🫰✨ Thanks @vctrchu! Your snapshots have been published to npm.

Test the snapshots by updating your package.json with the newly published versions:

"@shopify/data-extensions": "0.0.0-snapshot-20241212204821",
"@shopify/ui-extensions": "0.0.0-snapshot-20241212204821",
"@shopify/ui-extensions-react": "0.0.0-snapshot-20241212204821"

[github-actions]

We detected some changes in packages/*/package.json or packages/*/src, and there are no updates in the .changeset directory. If the changes are user-facing and should cause a version bump, run yarn changeset to track your changes and include them in the next release CHANGELOG. If you are making simple updates to repo configuration, examples, or documentation, you do not need to add a changeset.