gh-158051: Update testbed to support Xcode 27

[freakboy3742]

Xcode 27 imposes a minimum iOS version on projects, and requires the use of a UIScene lifecycle.

This modifies the iOS testbed project to:

• bump the iOS target version (from 13.0 to 15.0, the new minimum)
• add a UIScene-based lifecycle to the app

Github Actions CI testing is currently performed with Xcode 26; Buildbot currently uses Xcode 16. I have manually tested this with Xcode 27 as well.

Marked for backport to all iOS-supporting versions, because otherwise it's going to be difficult to test old Python versions on a recent setup. #158018 flags a similar class of issue on Android; there's a bigger conversation to be had around this problem.

• Issue: iOS testbed incompatible with Xcode 27 #158051

[freakboy3742]

!buildbot iOS

[bedevere-bot]

🤖 New build scheduled with the buildbot fleet by @freakboy3742 for commit 1bc4638 🤖

Results will be shown at:

https://buildbot.python.org/all/#/grid?branch=refs%2Fpull%2F158052%2Fmerge

The command will test the builders whose names match following regular expression: iOS

The builders matched are:

• iOS ARM64 Simulator PR

[ned-deily]

Other than the .gitignore entry, LGTM. make testios ran successfully on Xcode 26 / macOS 26 and Xcode 27 / macOS 27 builds.

[ned-deily]

Is this intended?

[freakboy3742]

It was semi-intentional; /docs/superpowers is an AI-planning folder used by the Superpowers AI tool. I had some planning docs that were coming up as uncommitted files in git, so I figured I'd add it in. However, it's not essential for this change, so I can drop it.

[miss-islington-app]

Thanks @freakboy3742 for the PR 🌮🎉.. I'm working now to backport this PR to: 3.13, 3.14, 3.15.
🐍🍒⛏🤖

[miss-islington-app]

Sorry, @freakboy3742, I could not cleanly backport this to 3.14 due to a conflict.
Please backport using cherry_picker on command line.

cherry_picker daacd2d9a2b47ee277f398ed024afe6ced6f039f 3.14

[miss-islington-app]

Sorry, @freakboy3742, I could not cleanly backport this to 3.13 due to a conflict.
Please backport using cherry_picker on command line.

cherry_picker daacd2d9a2b47ee277f398ed024afe6ced6f039f 3.13

[bedevere-app]

GH-158060 is a backport of this pull request to the 3.15 branch.

[bedevere-app]

GH-158061 is a backport of this pull request to the 3.14 branch.

[bedevere-app]

GH-158062 is a backport of this pull request to the 3.13 branch.