Desugar parsing for <| and |> directly into function calls

[jfecher]

The tokens for these operators already exist: Token::ApplyLeft and Token::ApplyRight respectively.

|> should be left-associative with a precedence two levels under +
<| should be right-associative with a precedence one level under +

Support for these can be added in the parser such that
a |> foo b c |> bar d e parses as bar (foo a b c) d e
and
bar d e <| foo b c <| a also parses as bar (foo a b c) d e.

It would be nice if the parser desugared the operator directly into the above function calls so no further handling would need to be done in later passes.