Re-enable MacCatalyst IO tests disabled by issue 114403

[Copilot]

The macOS 12 → 14 CI queue migration surfaced MacCatalyst permission issues (Documents-folder pop-up in IsolatedStorage, ReadExecute SIGKILL in MemoryMappedFiles), which caused several IO tests to be disabled under issue 114403. This re-enables them so the macOS 14 queue can validate whether the issues persist.

Description

• System.IO.IsolatedStorage/tests/.../RemoveTests.cs — Removed the four [ActiveIssue(114403, IsMacCatalyst)] attributes on RemoveUserStoreForApplication, RemoveUserStoreForAssembly, RemoveUserStoreForDomain, and RemoveStoreWithContent.
• System.IO.MemoryMappedFiles/tests/MemoryMappedViewAccessor.Tests.cs and MemoryMappedViewStream.Tests.cs — Dropped the PlatformDetection.IsNotMacCatalyst guard so the ReadExecute/ReadExecute combination is exercised again on MacCatalyst:

yield return new object[] { MemoryMappedFileAccess.ReadExecute, MemoryMappedFileAccess.CopyOnWrite };
yield return new object[] { MemoryMappedFileAccess.ReadExecute, MemoryMappedFileAccess.ReadExecute };
yield return new object[] { MemoryMappedFileAccess.CopyOnWrite, MemoryMappedFileAccess.Read };

PlatformDetection remains referenced elsewhere in both MemoryMappedFiles test files. These are test-only changes; the MacCatalyst CI legs are the actual signal for whether the underlying permission/signature issues are resolved.

• Fixes [infra][maccatalyst] Fix IO test compatibility issues occurring on MacCatalyst CI with macOS 14 #114403

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/azp run runtime-ioslike

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