PixelPaint: Add ProjectLoader to abstract away opening of files

This new class will open and parse files (either images directly or .pp
project files) and one can get the parsed Image as well as other
information from it.

This patch removes a bunch of 'try_create_from..." methods from Image in
favor of using the ProjectLoader.

The only json_metadata that is available are Guides for now.

Userland/Applications/PixelPaint/ProjectLoader.h

@@ -0,0 +1,35 @@
+/*
+ * Copyright (c) 2021, Tobias Christiansen <tobyase@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include "Image.h"
+#include <AK/JsonArray.h>
+#include <AK/Result.h>
+#include <AK/StringView.h>
+
+namespace PixelPaint {
+
+class ProjectLoader {
+public:
+    ProjectLoader() = default;
+    ~ProjectLoader() = default;
+
+    Result<void, String> try_load_from_fd_and_close(int fd, StringView path);
+    Result<void, String> try_load_from_path(StringView path);
+
+    bool is_raw_image() const { return m_is_raw_image; }
+    bool has_image() const { return !m_image.is_null(); }
+    RefPtr<Image> release_image() const { return move(m_image); }
+    JsonArray const& json_metadata() const { return m_json_metadata; }
+
+private:
+    RefPtr<Image> m_image { nullptr };
+    bool m_is_raw_image { false };
+    JsonArray m_json_metadata {};
+};
+
+}