Kernel/Devices: Defer creation of SysFS component after the constructor

Instead of doing so in the constructor, let's do immediately after the
constructor, so we can safely pass a reference of a Device, so the
SysFSDeviceComponent constructor can use that object to identify whether
it's a block device or a character device.
This allows to us to not hold a device in SysFSDeviceComponent with a
RefPtr.
Also, we also call the before_removing method in both SlavePTY::unref
and File::unref, so because Device has that method being overrided, it
can ensure the device is removed always cleanly.

Kernel/Graphics/FramebufferDevice.cpp

@@ -22,7 +22,10 @@ namespace Kernel {
 
 NonnullRefPtr<FramebufferDevice> FramebufferDevice::create(const GraphicsDevice& adapter, size_t output_port_index, PhysicalAddress paddr, size_t width, size_t height, size_t pitch)
 {
-    return adopt_ref(*new FramebufferDevice(adapter, output_port_index, paddr, width, height, pitch));
+    auto framebuffer_device_or_error = try_create_device<FramebufferDevice>(adapter, output_port_index, paddr, width, height, pitch);
+    // FIXME: Find a way to propagate errors
+    VERIFY(!framebuffer_device_or_error.is_error());
+    return framebuffer_device_or_error.release_value();
 }
 
 KResultOr<Memory::Region*> FramebufferDevice::mmap(Process& process, OpenFileDescription&, Memory::VirtualRange const& range, u64 offset, int prot, bool shared)

Kernel/Graphics/FramebufferDevice.h

@@ -32,6 +32,9 @@ public:
     virtual ~FramebufferDevice() {};
     KResult initialize();
 
+    // FIXME: We expose this constructor to make try_create_device helper to work
+    FramebufferDevice(const GraphicsDevice&, size_t, PhysicalAddress, size_t, size_t, size_t);
+
 private:
     // ^File
     virtual StringView class_name() const override { return "FramebufferDevice"; }
@@ -42,8 +45,6 @@ private:
     virtual KResultOr<size_t> read(OpenFileDescription&, u64, UserOrKernelBuffer&, size_t) override { return EINVAL; }
     virtual KResultOr<size_t> write(OpenFileDescription&, u64, const UserOrKernelBuffer&, size_t) override { return EINVAL; }
 
-    FramebufferDevice(const GraphicsDevice&, size_t, PhysicalAddress, size_t, size_t, size_t);
-
     PhysicalAddress m_framebuffer_address;
     size_t m_framebuffer_pitch { 0 };
     size_t m_framebuffer_width { 0 };

Kernel/Graphics/VirtIOGPU/GPU.cpp

@@ -64,6 +64,7 @@ void GPU::create_framebuffer_devices()
     for (size_t i = 0; i < min(m_num_scanouts, VIRTIO_GPU_MAX_SCANOUTS); i++) {
         auto& scanout = m_scanouts[i];
         scanout.framebuffer = adopt_ref(*new VirtIOGPU::FrameBufferDevice(*this, i));
+        scanout.framebuffer->after_inserting();
         scanout.console = Kernel::Graphics::VirtIOGPU::Console::initialize(scanout.framebuffer);
     }
 }