Proposal: raise the minimum supported Xcode version to Xcode 26

We plan to raise this SDK’s minimum supported build toolchain to **Xcode 26**.

Apple now requires App Store Connect submissions to be [built with Xcode 26 or later and an iOS 26 SDK or later](https://developer.apple.com/news/upcoming-requirements/?id=04282026a). This lets us remove legacy Xcode/SDK compatibility code, older CI coverage, and workarounds that no longer serve App Store builds.

This is a request for concrete blockers before we make the change.

Please comment if you still need an older Xcode version, including:

- the oldest Xcode version you need;
- whether the app is distributed through the App Store, Enterprise/MDM, internal distribution, or another channel;
- why upgrading is blocked; and
- the specific SDK feature or integration that prevents the upgrade.