Tests an issue where pattern matching matrices involving built-in
types was discarding default cases in some branches.

``` unison
f = cases
  0, 0 -> 0
  _, 1 -> 2
  1, _ -> 3
  _, _ -> 1

> f 0 0
> f 1 0
> f 0 1
> f 1 1
```

``` ucm

  Loading changes detected in scratch.u.

  I found and typechecked these definitions in scratch.u. If you
  do an `add` or `update`, here's how your codebase would
  change:
  
    ⍟ These new definitions are ok to `add`:
    
      f : Nat -> Nat -> Nat
  
  Now evaluating any watch expressions (lines starting with
  `>`)... Ctrl+C cancels.

    7 | > f 0 0
          ⧩
          0
  
    8 | > f 1 0
          ⧩
          3
  
    9 | > f 0 1
          ⧩
          2
  
    10 | > f 1 1
           ⧩
           2

```