1. Instead of getting the `FULL_PRODUCT_NAME` Xcode build setting (`Runner.app`) instead use `PRODUCT_NAME` since most places really want the product name, and the extension stripping wasn't correct when the name contained periods.
2. Don't instruct the user to open the `xcarchive` in Xcode if it doesn't exist.
Fixes https://github.com/flutter/flutter/issues/140212