LibDeviceTree: Add a simple DeviceTree class

This makes it easier to work with device tree nodes and properties, then
writing simple state machines to parse the device tree.
This also makes the old slow traversal methods use the
DeviceTreeProperty helper class, and adds a simple test.

Tests/LibDeviceTree/TestLookup.cpp

@@ -0,0 +1,29 @@
+/*
+ * Copyright (c) 2024, Leon Albrecht <leon.a@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <LibTest/TestCase.h>
+
+#include <LibCore/File.h>
+#include <LibCore/System.h>
+#include <LibDeviceTree/DeviceTree.h>
+#include <LibDeviceTree/FlattenedDeviceTree.h>
+
+TEST_CASE(basic_functionality)
+{
+    auto fdt_file = TRY_OR_FAIL(Core::File::open("/usr/Tests/LibDeviceTree/dtb.dtb"sv, Core::File::OpenMode::Read));
+    auto fdt = TRY_OR_FAIL(fdt_file->read_until_eof());
+
+    auto device_tree = TRY_OR_FAIL(DeviceTree::DeviceTree::parse(fdt));
+
+    auto boot_args = device_tree->resolve_property("/chosen/bootargs"sv);
+    EXPECT(boot_args.has_value());
+    EXPECT_EQ(boot_args->as_string(), "hello root=nvme0:1:0 serial_debug"sv);
+
+    EXPECT(device_tree->phandle(1));
+    auto device_type = device_tree->phandle(1)->get_property("device_type"sv);
+    EXPECT(device_type.has_value());
+    EXPECT_EQ(device_type->as_string(), "cpu"sv);
+}