PR Summary

SomeSystemPolicy APIs are useful outside of PowerShell, for example, theThreadJob module depends on them to determine when to block a thread job from running. However, they are not included in thePowerShellStandard.Library package because they are Windows-only API so far. So, it's hard for a module to use it -- it has to invoke those method with reflection.

In order to include them in thePowerShellStandard.Library package, those APIs need to be available on both Windows and Unix platforms, so this PR make them visible but non-op on Unix, so that they can be included inPowerShellStandard.Library the next time we update that package.

classSystemPolicy{publicstaticSystemEnforcementModeGetSystemLockdownPolicy();publicstaticSystemEnforcementModeGetLockdownPolicy(stringpath,SafeHandlehandle);publicstaticSystemScriptFileEnforcementGetFilePolicyEnforcement(stringfilePath,FileStreamfileStream);}

[Update] As pointed out in#25051 (comment), theGetFilePolicyEnforcement method is not available in Windows 5.1 on Win10 or Windows Server 2022. So, we probably should only includeGetSystemLockdownPolicy andGetLockdownPolicy inPowerShellStandard.Library for the short/middle term. After Windows 10 and Windows Server 2022 reach EOL (or when the method becomes available on them) we can then add theGetFilePolicyEnforcement method to the package.

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