Discover SwiftPM interface builder files in target sources

[ileitch]

Summary

Fix SwiftPM Interface Builder discovery by scanning target directories for XIB and storyboard files, even when they are not declared as package resources.
Add regression coverage for private IBAction methods and the fallback filesystem discovery path.

Made with Cursor

[Copilot]

Pull request overview

Fixes SwiftPM Interface Builder discovery by augmenting SPM planning to find .xib/.storyboard files via filesystem scanning of target directories (not just declared resources), and adds regression tests to cover private IBAction handling and the fallback discovery path.

Changes:

• Extend SPMProjectDriver to collect Interface Builder files by enumerating each target’s directory for .xib/.storyboard files.
• Add macOS regression coverage for (a) private/private-extension IBAction methods referenced from XIBs and (b) discovery when resources aren’t declared in the SwiftPM manifest.
• Update the macOS SwiftPM fixture XIB and controller to include a connected IBAction in a private extension.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
Tests/SPMTests/SPMProjectMacOSTest.swift	Adds a new regression test that drives SPMProjectDriver using a minimal manifest JSON and validates XIB discovery + reference retention.
Tests/SPMTests/SPMProjectMacOS/Sources/SPMProjectMacOSKit/SPMXibViewController.swift	Makes IBAction methods private and adds private-extension IBActions for retention/regression coverage.
Tests/SPMTests/SPMProjectMacOS/Sources/SPMProjectMacOSKit/Resources/SPMXibViewController.xib	Connects a new IBAction selector to the view controller to validate private-extension action discovery.
Sources/ProjectDrivers/SPMProjectDriver.swift	Implements filesystem-based Interface Builder file discovery within SwiftPM target directories.

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