Switch PrintType.re to syntax outcome printer.

[IwanKaramazow]

PrintType.re currently uses some custom code to print types. The outcome printer from the syntax repo implements the same functionality: https://github.com/rescript-lang/syntax/blob/master/src/res_outcome_printer.ml and has tests.
To reduce complexity and provide a better printing experience for the user we should switch to the outcome printer of the syntax repo. Types can be converted to the Outcometree with the compiler-libs if I recall correctly.

[amiralies]

Should we use syntax repo as a submodule for this or just vendor desired modules?

[cristianoc]

The missing cases currently fall back to Printtyp.type_expr, which is implemented in the compiler as:

let typexp sch ppf ty =
  !Oprint.out_type ppf (tree_of_typexp sch ty)

let type_expr ppf ty = typexp false ppf ty

So one would use the same logic but replace Oprint.out_type.