Utilities+Base: Add unveil utility

This utility essentially creates a filesystem sandbox for a specified
command, so it can be tested with only the unveiled paths the user
specifies beforehand.

Userland/Utilities/unveil.cpp

@@ -0,0 +1,38 @@
+/*
+ * Copyright (c) 2022, Liav A. <liavalb@hotmail.co.il>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <LibCore/ArgsParser.h>
+#include <LibCore/File.h>
+#include <LibCore/MappedFile.h>
+#include <LibCore/System.h>
+#include <LibELF/Image.h>
+#include <LibMain/Main.h>
+
+ErrorOr<int> serenity_main(Main::Arguments arguments)
+{
+    Vector<String> unveil_paths;
+    Vector<StringView> command;
+
+    Core::ArgsParser args_parser;
+    args_parser.set_stop_on_first_non_option(true);
+    args_parser.add_option(unveil_paths, "Path to unveil [permissions,path]", "path", 'u', "");
+    args_parser.add_positional_argument(command, "Command to execute", "command");
+    args_parser.parse(arguments);
+
+    if (unveil_paths.is_empty()) {
+        return Error::from_string_view("No unveil paths were specified."sv);
+    }
+
+    for (auto& path : unveil_paths) {
+        auto parts = path.split_view(',');
+        if (parts.size() != 2)
+            return Error::from_string_literal("Unveil path being specified is invalid.");
+        TRY(Core::System::unveil_after_exec(parts[1], parts[0]));
+    }
+
+    TRY(Core::System::exec(command[0], command, Core::System::SearchInPath::Yes));
+    return 0;
+}