PR Summary

Fix #15958
Fix #13365

Change Target from a CodeProperty to be an AliasProperty that points to FileSystemInfo.LinkTarget.
Also, keep the public API InternalSymbolicLinkLinkCodeMethods.GetTarget(PSObject instance), but use FileSystemInfo.LinkTarget inside.

I have reviewed the .NET implementation of LinkTarget, and can confirm that the functionality is in parity.
The only difference is that LinkTarget doesn't throw error when the file doesn't exist, but our GetTarget(...) throws exception in that case. So, I add the file-existence check at some places, and other places doesn't need the check.

It would be easier to review by ignoring the white-space changes:
https://github.com/PowerShell/PowerShell/pull/16165/files?w=1

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