Kernel/SysFS: Add exposing interface for DisplayConnectors

Under normal conditions (when mounting SysFS in /sys), there will be a
new directory in the /sys/devices directory called "graphics".
For now, under that directory there will be only a sub-directory called
"connectors" which will contain all DisplayConnectors' details, each in
its own sub-directory too, distinguished in naming with its minor
number.

Therefore, /sys/devices/graphics/connectors/MINOR_NUMBER/ will contain:
- General device attributes such as mutable_mode_setting_capable,
  double_buffering_capable, flush_support, partial_flush_support and
  refresh_rate_support. These values are exposed in the ioctl interface
  of the DisplayConnector class too, but these can be useful later on
  for command line utilities that want/need to expose these basic
  settings.
- The EDID blob, simply named "edid". This will help userspace to fetch
  the edid without the need of using the ioctl interface later on.

Kernel/FileSystem/SysFS/Subsystems/Devices/Graphics/DisplayConnector/DeviceAttribute.h

@@ -0,0 +1,42 @@
+/*
+ * Copyright (c) 2022, Liav A. <liavalb@hotmail.co.il>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <Kernel/FileSystem/SysFS/Component.h>
+#include <Kernel/FileSystem/SysFS/Subsystems/Devices/Graphics/DisplayConnector/DeviceDirectory.h>
+#include <Kernel/Graphics/DisplayConnector.h>
+#include <Kernel/KBuffer.h>
+
+namespace Kernel {
+
+class DisplayConnectorAttributeSysFSComponent : public SysFSComponent {
+public:
+    enum class Type {
+        MutableModeSettingCapable,
+        DoubleFrameBufferingCapable,
+        FlushSupport,
+        PartialFlushSupport,
+        RefreshRateSupport,
+        EDID,
+    };
+
+public:
+    static NonnullRefPtr<DisplayConnectorAttributeSysFSComponent> must_create(DisplayConnectorSysFSDirectory const& device_directory, Type);
+
+    virtual ErrorOr<size_t> read_bytes(off_t, size_t, UserOrKernelBuffer&, OpenFileDescription*) const override;
+    virtual ~DisplayConnectorAttributeSysFSComponent() {};
+
+    virtual StringView name() const override;
+
+protected:
+    ErrorOr<NonnullOwnPtr<KBuffer>> try_to_generate_buffer() const;
+    DisplayConnectorAttributeSysFSComponent(DisplayConnectorSysFSDirectory const& device, Type);
+    NonnullRefPtr<DisplayConnector> m_device;
+    Type const m_type { Type::MutableModeSettingCapable };
+};
+
+}