Add support for record selector syntax for tupes for CakeML

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*)
```