This commit adds a `mipmaps` member to the `GPUTexture` struct and also computes to the memory used by these mipmaps and the memory used for textures that are created from an external bindcode. So it solves the following inconsistencies: - The memory value for mipmaps was not being computed. - As `GPU_texture_from_bindcode` didn't call `gpu_texture_memory_footprint_add`, it brought inconsistencies to the value of the used memory, especially when the texture is freed. Differential Revision: https://developer.blender.org/D3554