Fix clone ownership under Windows Administrator Protection

[tyrielv]

Problem

Under Windows Administrator protection (AP), an elevated process runs as a hidden, profile-separated shadow admin account (MACHINE\admin_<user>) whose SID is a local account (S-1-5-21-…) that differs from the real, non-elevated user's SID.

When gvfs clone runs elevated, the enlistment's src and .git directories are created owned by the Administrators group. EnsureDirectoryIsOwnedByCurrentUser then reassigned ownership to the current user to satisfy git's dubious-ownership check. Under AP the "current user" is the shadow admin, so ownership was set to admin_<user>.

The real (non-elevated) user then hits:

fatal: detected dubious ownership in repository

because git's Administrators-group-membership grace does not cover another specific user's SID, and the shadow admin cannot SetOwner to the real user's SID either.

Fix

Detect AP via HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\System!TypeOfAdminApprovalMode == 2. When AP is active, leave the directory owner as the Administrators group instead of reassigning it to the shadow admin.

An Administrators-owned directory is accepted by modern git and the libgit2 non-elevated-admin-owner overlay for any Administrators member — the real user, the shadow admin, and SYSTEM (for automount) alike. So skipping the reassignment under AP is correct for every consumer.

When AP is not active, behavior is unchanged (owner reassigned to the current user, as before).

Changes

• GVFS.Platform.Windows/WindowsPlatform.cs — add IsAdminApprovalModeEnabled() (reads TypeOfAdminApprovalMode).
• GVFS.Platform.Windows/WindowsFileSystem.cs — in EnsureDirectoryIsOwnedByCurrentUser, skip the Administrators→current-user reassignment when AP is active.

Testing

• Builds clean (GVFS.Platform.Windows, 0 warnings / 0 errors).
• Manual validation under a real AP machine is pending (requires enabling AP + reboot). The AP constraints this fix relies on were empirically verified on an AP machine in prior investigation.

Related

• Follow-up to the SpringBoard DoubleCheck AP change (ADO PR 16074604, AB#62918022) — this PR owns the GVFS/VFSForGit side.
• Original elevated-clone ownership fix: Fix ownership when cloning elevated #1829 (4e23d28a).