`as_integers` and `as_doubles` should understand logical inputs

[vspinu]

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Arguably logicals are also "integer like", but the main use case is the all-NA input vectors. When a user enters xyz(arg = NA) and arg is intended to be an integer the cpp level conversion with as_integers fails.

For this reason as_integers is still incomplete because we still need a custom wrapper around as_integer for logicals internally.

Would be really great if it could be done as part of #265 (cc @DavisVaughan)

[pachadotdev]

@vspinu @DavisVaughan

I implemented 25% of this. I say 25% and not 50% because I do not like the implementation as I could not find a good way to use

std::transform(xn.begin(), xn.end() ...

with logicals

here is the draft https://github.com/r-lib/cpp11/pull/426