TextureSlice mess vulkan backend copyTexture implement.

[HuazyYang]

struct TextureSlice
    {
        uint32_t x = 0;
        uint32_t y = 0;
        uint32_t z = 0;
        // -1 means the entire dimension is part of the region
        // resolve() below will translate these values into actual dimensions
        uint32_t width = uint32_t(-1);
        uint32_t height = uint32_t(-1);
        uint32_t depth = uint32_t(-1);
};

TextureSlice confuse texture subresource dimmension info and texture copy box concept completely. For GAPI concept, copy texture can use different destination texel coordinate (x, y, z) and source box region (left, top, front, right, bottom, back), but TextureSlice just confuse this two different concept when using width, height, depth field as box region dimensions and texture subresource dimension.

For API desgin decision, copyTexture API should not use TextureSlice as an input parameter. copyTexture need 6 parameters:

• destination resource handle;
• destination subresource indices (mipSlice, arraySlice);
• destination texel coordinate inside subresource (dstX, dstY, dstZ)
• source resource handle;
• source subresource indices (mipSlice, arraySlice);
• copied texel box region inside the subresource (left, top, front, right, bottom, back)

Wrap parameters to a common structure is a choise but not a better practise.