[release/8.0-staging] Support setting ACLs on file paths longer than MAX_PATH

[github-actions]

Backport of #92460 to release/8.0-staging

/cc @jeffhandley @karakasa @adamsitnik

Customer Impact

• Customer reported
• Found internally

Customer @AliveDevil requested this fix be backported to the LTS .NET 8 release, with the following comments:

Currently in the process of migrating a codebase from .NET framework to .NET 8 due to .NET Framework not handling long paths correctly. When .NET 8 doesn’t support long paths like this, there’s no point in going forward, as the next possible LTS version is 10 at the end of 2025.

Scenario is a file synchronization tool, which sets Acls on files, based on remote attributes. As a workaround I’ve used reflection and a lambdaexpression to get access to the Persist(string) overload, to call that directly with the \?-prefix.

Regression

• Yes
• No

Testing

This fix was merged into .NET 9 in September 2023, and has been in place since Preview 1. A new unit test was added as part of the original fix, and the fix also reuses an existing approach and PathInternal.EnsureExtendedPrefixIfNeeded helper method.

Risk

Low. Targeted fix for the specific ACL scenario.

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