[zd3d12] more helper functions

[Pyrolistical]

Added helpers:

1. fn checkFeatureSupport(gctx: *GraphicsContext, comptime feature: d3d12.FEATURE, data: anytype) HResultError!void
   Purpose: Compile time check to ensure correct data is passed in for feature.
   HResultError instead of HRESULT.
2. fn allocRenderTargetView(gctx: *GraphicsContext, handle: ResourceHandle, desc: ?*const d3d12.RENDER_TARGET_VIEW_DESC) d3d12.CPU_DESCRIPTOR_HANDLE
   Purpose: Use zd3d12.ResourceHandle instead of d3d12.IResource. Allocate required .RTV cpu descriptor and returns it.
3. fn allocDepthStencilView(gctx: *GraphicsContext, handle: ResourceHandle, desc: ?*const d3d12.DEPTH_STENCIL_VIEW_DESC) d3d12.CPU_DESCRIPTOR_HANDLE
   Purpose: Use zd3d12.ResourceHandle instead of d3d12.IResource. Allocate required .DSV cpu descriptor and returns it.
4. fn createRootSignature(gctx: *GraphicsContext, node_mask: w32.UINT, signature: *d3d.IBlob) HResultError!*d3d12.IRootSignature
   Purpose: Take in signature IBlob instead of pointer and size. Return *IRootSignature instead of out pointer. HResultError instead of HRESULT.
5. fn writeResource(gctx: *GraphicsContext, comptime T: type, destination: ResourceHandle, source: []const T) HResultError!void
   Purpose: Simplify writing a slice to a resource instead of manually mapping and unmapping a byte array.
6. fn clearRenderTargetView(gctx: *GraphicsContext, rt_view: d3d12.CPU_DESCRIPTOR_HANDLE, rgba: *const [4]w32.FLOAT, rects: []const w32.RECT) void
   Purpose: RECT slice instead of a length and pointer.
7. fn clearDepthStencilView(gctx: *GraphicsContext, ds_view: d3d12.CPU_DESCRIPTOR_HANDLE, clear_flags: d3d12.CLEAR_FLAGS, depth: w32.FLOAT, stencil: w32.UINT8, rects: []const w32.RECT) void
   Purpose: RECT slice instead of a length and pointer.
8. fn omSetRenderTargets(gctx: *GraphicsContext, render_target_descriptors: []const d3d12.CPU_DESCRIPTOR_HANDLE, single_handle: bool, ds_descriptors: ?*const d3d12.CPU_DESCRIPTOR_HANDLE) void
   Purpose: CPU_DESCRIPTOR_HANDLE slice instead of a length and pointer. bool instead of BOOL.
9. fn rsSetViewports(gctx: *GraphicsContext, viewports: []const d3d12.VIEWPORT)
   Purpose: VIEWPORT slice instead of a length and pointer.
10. fn rsSetScissorRects(gctx: *GraphicsContext, rects: []const d3d12.RECT)
    Purpose: RECT slice instead of a length and pointer.
11. fn iaSetPrimitiveTopology(gctx: *GraphicsContext, topology: d3d12.PRIMITIVE_TOPOLOGY) void
    Purpose: Passthrough to get rid of last usage of gctx.cmdlist in simple_openvr sample
12. fn iaSetVertexBuffers(gctx: *GraphicsContext, start_slot: w32.UINT, views: []const d3d12.VERTEX_BUFFER_VIEW)
    Purpose: VERTEX_BUFFER_VIEW slice instead of a length and pointer.
13. fn iaSetIndexBuffer(gctx: *GraphicsContext, view: ?*const d3d12.INDEX_BUFFER_VIEW) void
    Purpose: Passthrough to get rid of last usage of gctx.cmdlist in simple_openvr sample
14. fn setGraphicsRootConstantBufferView(gctx: *GraphicsContext, index: w32.UINT, handle: ResourceHandle) void
    Purpose: zd3d12.ResourceHandle instead of d3d12.IResource.
15. fn drawInstanced(gctx: *GraphicsContext, vertex_count_per_instance: w32.UINT, instance_count: w32.UINT, start_vertex_location: w32.UINT, start_instance_location: w32.UINT) void
    Purpose: Passthrough to get rid of last usage of gctx.cmdlist in simple_openvr sample
16. fn drawIndexedInstanced(gctx: *GraphicsContext, index_count_per_instance: w32.UINT, instance_count: w32.UINT, start_index_location: w32.UINT, base_vertex_location: w32.INT, start_instance_location: w32.UINT) void
    Purpose: Passthrough to get rid of last usage of gctx.cmdlist in simple_openvr sample
17. fn serializeVersionedRootSignature(root_signature_desc: *const d3d12.VERSIONED_ROOT_SIGNATURE_DESC) HResultError!*d3d.IBlob
    Purpose: Returns IBlob instead of out pointer. HResultError instead of HRESULT.