GPURenderState inconsistencies with the GPU API

[ritalat]

The recently added SDL GPU extension for the 2D Render API has some inconsistencies with GPU API conventions:

• The GPU API uses Vulkan-ish *CreateInfo structures but the SDL_CreateGPURenderState equivalent is named SDL_GPURenderStateDesc instead
• Said SDL_GPURenderStateDesc is versioned and must be initialized with SDL_INIT_INTERFACE, while the GPU API *CreateInfo structures have a field for extension properties instead (see SDL_GPUShaderCreateInfo)
• SDL_SetRenderGPUState should be named SDL_SetGPURenderState(?); all other GPU related renderer functions or structures are named in the style of *GPURender*