[net8.0] [build] Require using EnablePreviewFeatures=true when using preview releases. Contributes towards #18343.

[rolfbjarne]

Detect if we're using a non-stable Xcode, and in that case produce packages
that show an error if they're used and the EnablePreviewFeatures flag isn't
enabled.

Also add logic to set this flag for our own build, otherwise all our tests
would fail.

This is the same as Android does.

Contributes towards #18343.

[vs-mobiletools-engineering-service2]

💻 [CI Build] Windows Integration Tests passed 💻

✅ All Windows Integration Tests passed.

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• xamarin.ios-16.5.0.560.pkg
• xamarin.mac-9.4.0.560.pkg

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[vs-mobiletools-engineering-service2]

❌ [PR Build] Tests on macOS M1 - Mac Ventura (13.0) failed ❌

Failed tests are:

• linksdk
• monotouch-test

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[vs-mobiletools-engineering-service2]

❌ [PR Build] Tests on macOS M1 - Mac Big Sur (11.5) failed ❌

Failed tests are:

• linksdk
• monotouch-test

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[vs-mobiletools-engineering-service2]

✅ API diff for current PR / commit

NET (empty diffs)

• iOS: (empty diff detected)
• tvOS: (empty diff detected)
• MacCatalyst: (empty diff detected)
• macOS: (empty diff detected)

✅ API diff vs stable

.NET (No breaking changes)

• iOS: vsdrops gist (No breaking changes)
• tvOS: vsdrops gist (No breaking changes)
• MacCatalyst: vsdrops gist (No breaking changes)
• macOS: vsdrops gist (No breaking changes)
• Microsoft.iOS vs Microsoft.MacCatalyst: vsdrops gist

ℹ️ Generator diff

Generator Diff: vsdrops (html) vsdrops (raw diff) gist (raw diff) - Please review changes)

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🚀 [CI Build] Test results 🚀

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✅ All tests passed on VSTS: simulator tests.

🎉 All 89 tests passed 🎉

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⚠️ bcl: No tests selected. Html Report (VSDrops) Download
✅ cecil: All 1 tests passed. Html Report (VSDrops) Download
✅ dotnettests: All 1 tests passed. [attempt 3] Html Report (VSDrops) Download
✅ fsharp: All 4 tests passed. Html Report (VSDrops) Download
✅ framework: All 4 tests passed. Html Report (VSDrops) Download
✅ generator: All 1 tests passed. Html Report (VSDrops) Download
✅ interdependent_binding_projects: All 4 tests passed. Html Report (VSDrops) Download
⚠️ install_source: No tests selected. Html Report (VSDrops) Download
✅ introspection: All 4 tests passed. Html Report (VSDrops) Download
✅ linker: All 40 tests passed. Html Report (VSDrops) Download
⚠️ mac_binding_project: No tests selected. Html Report (VSDrops) Download
⚠️ mmp: No tests selected. Html Report (VSDrops) Download
⚠️ mononative: No tests selected. Html Report (VSDrops) Download
✅ monotouch: All 23 tests passed. [attempt 2] Html Report (VSDrops) Download
✅ msbuild: All 2 tests passed. Html Report (VSDrops) Download
⚠️ mtouch: No tests selected. Html Report (VSDrops) Download
⚠️ xammac: No tests selected. Html Report (VSDrops) Download
✅ xcframework: All 4 tests passed. Html Report (VSDrops) Download
✅ xtro: All 1 tests passed. Html Report (VSDrops) Download

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