refactor all random functions to use applyreduce

[asinghvi17]

No description provided.

[rafaqz]

E.g. flatten, unwrap, reconstruct

[asinghvi17]

I think only flatten can be done this way - here's how:

function _flatten(f, target, geoms)
	return applyreduce(f, vcat, target, geoms)
end

(I think)

[rafaqz]

I think even apply itself can just use applyreduce! - or they can all share a more generic/abstract function.

I like the idea of having just one GeoInterface walker

[asinghvi17]

Yeah agreed, we should do that. What's the best approach though? I had considered having an Apply struct, which carries the decompose, operate and reconstruct functions as type parameters. This could then have pretty flexible dispatch.

The other alternative is to have an apply iterator, but that would be hard to thread.