Refactor descriptor handling and shader compilation

Refactored descriptor allocation and release logic by introducing `IDescriptorAllocator` and replacing `DescriptorHeapAllocator` with `D3D12DescriptorHeap`. Updated descriptor structs to include validation properties and improved memory management with `ReadOnlySpan`.

Enhanced shader compilation by introducing `ShaderStage` and `CompilerVersion` enums, enabling more flexible and maintainable shader handling.

Refactored `Mesh` to use `IBuffer` for vertex and index buffers, added bindless descriptor support, and improved resource cleanup.

Updated `RenderSystem` and other components for better initialization, error handling, and disposal logic. General improvements to code readability and maintainability.

Ghost.Graphics/Data/Descriptors.cs

@@ -0,0 +1,78 @@
+using Win32.Graphics.Direct3D12;
+
+namespace Ghost.Graphics.Data;
+
+/// <summary>
+/// Render target view (RTV) descriptor.
+/// </summary>
+public readonly struct RenderTargetDescriptor
+{
+    public uint Index
+    {
+        get; init;
+    }
+
+    public static RenderTargetDescriptor Invalid => new() { Index = ~0u };
+
+    public bool IsValid => Index != ~0u;
+}
+
+/// <summary>
+/// Depth stencil view (DSV) descriptor.
+/// </summary>
+public readonly struct DepthStencilDescriptor
+{
+    public uint Index
+    {
+        get; init;
+    }
+
+    public static DepthStencilDescriptor Invalid => new() { Index = ~0u };
+
+    public bool IsValid => Index != ~0u;
+}
+
+/// <summary>
+/// Shader resource view (SRV) descriptor.
+/// </summary>
+public readonly struct ShaderResourceDescriptor
+{
+    public uint Index
+    {
+        get; init;
+    }
+
+    public static ShaderResourceDescriptor Invalid => new() { Index = ~0u };
+
+    public bool IsValid => Index != ~0u;
+}
+
+/// <summary>
+/// Sampler descriptor.
+/// </summary>
+public readonly struct SamplerDescriptor
+{
+    public uint Index
+    {
+        get; init;
+    }
+
+    public static SamplerDescriptor Invalid => new() { Index = ~0u };
+
+    public bool IsValid => Index != ~0u;
+}
+
+/// <summary>
+/// Bindless descriptor
+/// </summary>
+public readonly struct BindlessDescriptor
+{
+    public uint Index
+    {
+        get; init;
+    }
+
+    public static BindlessDescriptor Invalid => new() { Index = ~0u };
+
+    public bool IsValid => Index != ~0u;
+}