Add SynType.Or.

[nojaf]

Hello,

We found a regression in Fantomas for:

let inline (!!) (x: ^a) : ^b = ((^a or ^b): (static member op_Implicit: ^a -> ^b) x)

I suspect the changes of #13119 could be related, but I'm not quite sure.

Our problem is that the parentheses around ^a or ^b are not stored in the syntax tree.
Nor, do we have any notion of the or keyword.

We would like to have information on both of these things in the syntax tree.

This additional information like this, allows us to restore these code comments.

(
 (// comment 1
  ^a 
     or // comment 2 
   ^b
  ) // comment 3
    : (static member op_Implicit: ^a -> ^b) x)

[nojaf]

Thank you @T-Gro and others for the reviews these past couple of days.
Much appreciated!

[T-Gro]

@psfinaki or @0101 , can one of you guys be the second reviewer here please ? :)

[0101]

@T-Gro I'll have a look at this tomorrow

[0101]

Looks good!

[nojaf]

Many thanks gentlemen!