Add shared helpers: ThrowIfFailed, ValidateNotNullOrEmpty, FindCmdlineTool

- ProcessUtils.ThrowIfFailed: consistent exit code checking with stderr/stdout context
- ProcessUtils.ValidateNotNullOrEmpty: reusable null/empty argument validation
- ProcessUtils.FindCmdlineTool: version-aware cmdline-tools directory search with legacy fallback

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: rmarinho

src/Xamarin.Android.Tools.AndroidSdk/ProcessUtils.cs

@@ -203,6 +203,73 @@ static string JoinArguments (string[] args)
 		}
 #endif
 
+		/// <summary>
+		/// Throws <see cref="InvalidOperationException"/> when <paramref name="exitCode"/> is non-zero.
+		/// Includes stderr/stdout context in the message when available.
+		/// </summary>
+		public static void ThrowIfFailed (int exitCode, string command, string? stderr = null, string? stdout = null)
+		{
+			if (exitCode == 0)
+				return;
+
+			var message = $"'{command}' failed with exit code {exitCode}.";
+
+			if (!string.IsNullOrEmpty (stderr))
+				message += $" stderr:{Environment.NewLine}{stderr!.Trim ()}";
+			if (!string.IsNullOrEmpty (stdout))
+				message += $" stdout:{Environment.NewLine}{stdout!.Trim ()}";
+
+			throw new InvalidOperationException (message);
+		}
+
+		/// <summary>
+		/// Validates that <paramref name="value"/> is not null or empty.
+		/// Throws <see cref="ArgumentNullException"/> for null values and
+		/// <see cref="ArgumentException"/> for empty strings.
+		/// </summary>
+		public static void ValidateNotNullOrEmpty (string? value, string paramName)
+		{
+			if (value is null)
+				throw new ArgumentNullException (paramName);
+			if (value.Length == 0)
+				throw new ArgumentException ("Value cannot be an empty string.", paramName);
+		}
+
+		/// <summary>
+		/// Searches versioned cmdline-tools directories (descending) and "latest" for a specific tool binary.
+		/// Falls back to the legacy tools/bin path. Returns null if not found.
+		/// </summary>
+		public static string? FindCmdlineTool (string sdkPath, string toolName, string extension)
+		{
+			var cmdlineToolsDir = Path.Combine (sdkPath, "cmdline-tools");
+
+			if (Directory.Exists (cmdlineToolsDir)) {
+				var subdirs = new List<(string name, Version? version)> ();
+				foreach (var dir in Directory.GetDirectories (cmdlineToolsDir)) {
+					var name = Path.GetFileName (dir);
+					if (string.IsNullOrEmpty (name) || name == "latest")
+						continue;
+					Version.TryParse (name, out var v);
+					subdirs.Add ((name, v ?? new Version (0, 0)));
+				}
+				subdirs.Sort ((a, b) => b.version!.CompareTo (a.version));
+
+				// Check versioned directories first (highest version first), then "latest"
+				foreach (var (name, _) in subdirs) {
+					var toolPath = Path.Combine (cmdlineToolsDir, name, "bin", toolName + extension);
+					if (File.Exists (toolPath))
+						return toolPath;
+				}
+				var latestPath = Path.Combine (cmdlineToolsDir, "latest", "bin", toolName + extension);
+				if (File.Exists (latestPath))
+					return latestPath;
+			}
+
+			// Legacy fallback: tools/bin/<tool>
+			var legacyPath = Path.Combine (sdkPath, "tools", "bin", toolName + extension);
+			return File.Exists (legacyPath) ? legacyPath : null;
+		}
+
 		internal static IEnumerable<string> FindExecutablesInPath (string executable)
 		{
 			var path        = Environment.GetEnvironmentVariable (EnvironmentVariableNames.Path) ?? "";