Retry MoveWithRollback on transient access errors from AV file scanning

[Copilot]

On Windows, FileUtil.MoveWithRollback intermittently fails with Access to the path '...' is denied because Defender's minifilter still holds read handles on files freshly written by ExtractZipSafe when Directory.Move runs immediately after. MoveFileExW requires exclusive access and surfaces this as UnauthorizedAccessException or IOException (sharing violation).

Changes (src/Xamarin.Android.Tools.AndroidSdk/FileUtil.cs)

• Retry with exponential backoff around the Directory.Move(sourcePath, targetPath) call inside MoveWithRollback. Up to 3 retries (4 attempts total) with delays 500ms → 1000ms → 2000ms.
• Retryable predicate matches only transient sharing-violation-style failures:
  • UnauthorizedAccessException
  • IOException whose HResult is ERROR_SHARING_VIOLATION (0x80070020) or ERROR_LOCK_VIOLATION (0x80070021). HResult is preferred over message matching since exception messages vary by locale and runtime.
  • Message substring "being used by another process" as a fallback for runtimes that don't populate HResult.
• Non-retryable exceptions (e.g. DirectoryNotFoundException) propagate immediately, so the existing backup/rollback path is unaffected.

static void MoveDirectoryWithRetry (string sourcePath, string targetPath, Action<TraceLevel, string> logger)
{
    const int maxRetries = 3;
    int delayMs = 500;
    for (int attempt = 0; ; attempt++) {
        try {
            Directory.Move (sourcePath, targetPath);
            return;
        }
        catch (Exception ex) when (attempt < maxRetries && IsRetryableMoveError (ex)) {
            logger (TraceLevel.Warning,
                $"Directory.Move failed (attempt {attempt + 1}/{maxRetries + 1}), retrying in {delayMs}ms: {ex.Message}");
            Thread.Sleep (delayMs);
            delayMs *= 2;
        }
    }
}

The retry is scoped to the move itself, so the caller does not need to re-download/re-extract the archive on a transient Defender race.

[jonathanpeppers]

This repo was moved to dotnet/android and this one will be archived shortly:

• Merge dotnet/android-tools into external/xamarin-android-tools with full history android#11998

Recreate this PR there if it is still needed, thanks!