Add options for Hlsl shader generator to allow register selection.

Hello,

in the current state OCIO does not allow generated code to manually specify register slots (d3d11/12):

Example of generated code :

`Texture2D ocio_lut1d_0;
SamplerState ocio_lut1d_0Sampler;`

This makes reflecting compiled shader (Nearly) mandatory to find the binding location, which is not desirable in many cases.

It would be nice to have an option to be able to set first register slot by hand, then get them generated in a fixed way, for example :

`shaderDesc->setLanguage(GPU_LANGUAGE_HLSL_DX11);
shaderDesc->setFunctionName(functionName);
shaderDesc->setResourceStartSlot(1);
shaderDesc->setSamplerStartSlot(4);

Generated code would become:

`Texture2D ocio_lut1d_0 : register(t1);
SamplerState ocio_lut1d_0Sampler : register(s4) `

On a later stage, supporting bindless for latest d3d12/vulkan implementations would also be nice.

Thanks
Julien

Localisez le générateur de shaders HLSL et les points d’entrée de gestion des options de ShaderDesc, puis examinez comment les déclarations de textures et de samplers sont générées. Ajoutez des slots de début configurables pour les ressources et les samplers, et vérifiez que le HLSL D3D11/D3D12 généré inclut les liaisons de registres demandées.

Rédigé par le modèle d'indexation à partir du texte de l'issue.