Canonical ordering for NamedTuple keys

@simeonschaub suggested

```julia
function canonicalize(nt::NamedTuple{_k,T}) where {_k,T}
if @generated
k = collect(_k)
sp = sortperm(k)
return quote
sp = ($(sp...),)
keys = ($(Meta.quot.(k[sp])...),)
types = Tuple{$(T.parameters[sp]...)}
NamedTuple{keys,types}(map(Base.Fix1(getfield, values(nt)), sp))
end
else
sp = sortperm(collect(keys(nt)))
return NamedTuple{keys(nt)[sp]}(values(nt)[sp])
end
end
```

_Originally posted by @simeonschaub in https://github.com/cscherrer/MeasureTheory.jl/issues/7#issuecomment-698863535_

We should have something like this in MeasureTheory.jl directly or use KeywordDispatch.jl. It looks like this shouldn't introduce much overhead, but let's keep an eye out for that anyway.