[release/6.0] CreateSymbolicLink PInvoke retval must be marshalled as U1

[jozkee]

Backport of #69150

Customer Impact

Customer reported. Customers who create Symbolic Links using the new APIs introduced in 6.0 will face silent failures when Developer mode is disabled in Windows settings.

File.Create("my-file.txt";).Dipose();

// Having developer mode disabled on Windows, this will silently fail.
FileSystemInfo linkInfo = File.CreateSymbolicLink("my-link", "my-file.txt"); 

Console.WriteLine($"Link exsts: {linkInfo.Exists}"); // prints false when it should’ve thrown above.

Testing

Customer confirmed and reported that issues is fixed, and it no longer fails silently.
The change has been in-place for months on .NET 7 with no failures involved.

Risk

Low, changes are minimal and self-evidently correct.

[ghost]

Tagging subscribers to this area: @dotnet/area-system-io
See info in area-owners.md if you want to be subscribed.

Issue Details

---

Backport of #69150

Customer Impact

Customers who create Symbolic Links using the new APIs introduced in 6.0 will face silent failures when Developer mode is disabled in Windows settings.

File.Create("my-file.txt";).Dipose();

// Having developer mode disabled on Windows, this will silently fail.
FileSystemInfo linkInfo = File.CreateSymbolicLink("my-link", "my-file.txt"); 

Console.WriteLine($"Link exsts: {linkInfo.Exists}"); // prints false when it should’ve thrown above.

Testing

Customer confirmed and reported that issues is fixed, and it no longer fails silently.
The change has been in-place for months on .NET 7 with no failures involved.

Risk

Low, changes are minimal.

Author:	Jozkee
Assignees:	Jozkee
Labels:	Servicing-consider, area-System.IO
Milestone:	6.0.x

[jozkee]

Failing runtime leg is an error on System.Diagnostics.Tests.PerformanceCounterTests, filed #73019.

runtime-staging shows many errors on
Build tvOSSimulator x64 Release AllSubsets_Mono,
Build iOSSimulator x64 Release AllSubsets_Mono,
Build Android x86 Release AllSubsets_Mono
and Build Browser wasm release Browser_wasm_Windows.

[adamsitnik]

[carlossanlop]

Tactics approved.
Correct milestone applied.
CI failures are unrelated.
Area owner signed off.
No OOB package authoring changes needed (affecting installer and Common code).
Ready to merge.