Support XCSkipTests under Mac Catalyst

[fhasse95]

This PR adds Mac Catalyst support to the Xcode Gradle test harness so XCSkipTests can be launched from Mac Catalyst test targets.

Since the JVM cannot load native libraries from Catalyst frameworks, the harness now performs a macOS host build of the tested package before invoking Gradle. It then passes the resulting SwiftPM build output directory to skip-ffi, allowing Robolectric to load the macOS host dylibs instead of the Catalyst framework binaries.

Related PRs:

• Load host FFI libraries for Mac Catalyst tests skip-ffi#11
• Support XCSkipTests under Mac Catalyst skipstone#265

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Please review the contribution guide at https://skip.dev/docs/contributing/ for advice and guidance on making high-quality PRs.

Skip Pull Request Checklist:

• REQUIRED: I have signed the Contributor Agreement
• REQUIRED: I have tested my change locally with swift test
• OPTIONAL: I have tested my change on an iOS simulator or device
• OPTIONAL: I have tested my change on an Android emulator or device

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• AI was used to generate or assist with generating this PR. Please specify below how you used AI to help you, and what steps you have taken to manually verify the changes.

AI was used to help identify the Catalyst/Robolectric host-library issue and draft the changes. Afterwards, I manually reviewed the code and verified the affected XCSkipTests from a Mac Catalyst test target.

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