Add shader-based image scaling modes

[ecton]

Currently image sampling is controlled purely through wgpu::FilterMode. We should add support for some common resizing kernels.

To do this, we need to determine a list of kernels we want to support. Reserve N bits on the u32 flags on PushConstants.

Next, we need to add API surfaces to allow users to specify a custom scaling mode when using draw texture calls. We must ensure this setting is passed through to the PushConstants::flags.

Inside of fragment the flags can be decoded to determine the proper kernel to use when sampling the texture. Once the sampled color is chosen, the blend color can be applied and returned.