More flexible interface for feature building

[odunbar]

Features could allow arg/distribution combination based on a different variety of distributions and constructions.

Idea

Introduce a FeatureArgType type so build_features can create more flexible types with a build_args function dispatching over ::FeatureArgType
E.g. informally building the the classic scalar feature would involve:

abstract type FeatureArgType
Affine <: FeatureArgType

function build_args(
    samp::sampler, 
    feature_parameters::Dict, 
    inputs::Array,
    ::Affine,
)
    xi = get_distribution(samp)["xi"] 
    uniform = get_distribution(samp)["uniform"]
   return inputs*xi + uniform
end

replacing the hardcoded

RandomFeatures.jl/src/Features.jl

Lines 148 to 156 in 2d864cc

	samp = get_feature_sample(rf)
	xi = get_distribution(samp)["xi"] # dim_inputs x n_features
	features = inputs * xi[:, batch_feature_idx] # n_samples x n_features
	is_uniform_shift = "uniform" ∈ get_name(samp)
	if is_uniform_shift
	uniform = get_distribution(samp)["uniform"] # 1 x n_features
	features .+= uniform[:, batch_feature_idx]
	end

• Possibly move the move the inbuilt uniform distribution elsewhere? It's only in the fourier case that this is necessary