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.cpp

@@ -0,0 +1,75 @@
+/*
+ * Copyright (c) 2021, Tobias Christiansen <tobyase@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include "ProjectLoader.h"
+#include "Image.h"
+#include "Layer.h"
+#include <AK/JsonObject.h>
+#include <AK/MappedFile.h>
+#include <AK/Result.h>
+#include <AK/String.h>
+#include <LibCore/File.h>
+#include <LibImageDecoderClient/Client.h>
+
+namespace PixelPaint {
+
+Result<void, String> ProjectLoader::try_load_from_fd_and_close(int fd, StringView path)
+{
+    auto file = Core::File::construct();
+    file->open(fd, Core::OpenMode::ReadOnly, Core::File::ShouldCloseFileDescriptor::No);
+    if (file->has_error())
+        return String { file->error_string() };
+
+    auto contents = file->read_all();
+
+    auto json_or_error = JsonValue::from_string(contents);
+    if (!json_or_error.has_value()) {
+        m_is_raw_image = true;
+
+        auto file_or_error = MappedFile::map_from_fd_and_close(fd, path);
+        if (file_or_error.is_error())
+            return String::formatted("Unable to mmap file {}", file_or_error.error().string());
+
+        auto& mapped_file = *file_or_error.value();
+        // FIXME: Find a way to avoid the memory copy here.
+        auto bitmap = Image::try_decode_bitmap(ByteBuffer::copy(mapped_file.bytes()));
+        if (!bitmap)
+            return String { "Unable to decode image"sv };
+        auto image = Image::try_create_from_bitmap(bitmap.release_nonnull());
+        if (!image)
+            return String { "Unable to allocate Image"sv };
+
+        image->set_path(path);
+        m_image = image;
+        return {};
+    }
+
+    close(fd);
+    auto& json = json_or_error.value().as_object();
+    auto image_or_error = Image::try_create_from_pixel_paint_json(json);
+
+    if (image_or_error.is_error())
+        return image_or_error.release_error();
+
+    auto image = image_or_error.release_value();
+    image->set_path(path);
+
+    if (json.has("guides"))
+        m_json_metadata = json.get("guides").as_array();
+
+    m_image = image;
+    return {};
+}
+Result<void, String> ProjectLoader::try_load_from_path(StringView path)
+{
+    auto file_or_error = Core::File::open(path, Core::OpenMode::ReadOnly);
+    if (file_or_error.is_error())
+        return String::formatted("Unable to open file because: {}", file_or_error.release_error());
+
+    return try_load_from_fd_and_close(file_or_error.release_value()->fd(), path);
+}
+
+}