Add support for record selector syntax for tupes for CakeML

[ordinarymath]

This issue is about adding support for record selector syntax for CakeML tuples. i.e. #1 (a,b). The main difficulty in implementing it is such that if a fixed tuple type is not found it should fail. examples.

fun a x = #1 x (*fails*)

fun a (x : 'a * 'b) = #1 x (*works*)