Fix Windows UNC path case-sensitivity resolution for network drives

[harrish243]

Description

This PR fixes Windows UNC path handling for network drives (\\\server\share\file\ and \\?\UNC\server\share\file).

Specifically:

• \RemoveUncPrefixMaybe: Properly strips Win32 device UNC prefix (\\?\UNC\\ or \\.\UNC\\ or \??\UNC\) to produce valid UNC network paths (\\\server\share\file).
• \AddUncPrefixMaybe: Correctly converts UNC network paths (\\\server\share\file) to extended-length Win32 device UNC paths (\\?\UNC\server\share\file).
• \IsAbsoluteNormalizedWindowsPath: Adds \HasUncNetworkPrefix\ check so network UNC paths are recognized as valid absolute normalized paths by functions like \GetLongPath, \IsSymlinkOrJunction, and \CreateJunction.

Motivation

Fixes issue with resolving and operating on UNC network drive paths on Windows.

Build API Changes

No

Checklist

• I have added tests for the new use cases (if any).
• I have updated the documentation (if applicable).

Release Notes

RELNOTES: Fix Windows UNC network path prefix handling (\\?\UNC\) and path normalization for network drives.

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