[Issue 23101] New: [std.sumtype] canMatch does not account ref

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=23101

          Issue ID: 23101
           Summary: [std.sumtype] canMatch does not account ref
           Product: D
           Version: D2
          Hardware: x86_64
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P1
         Component: phobos
          Assignee: nobody at puremagic.com
          Reporter: jlourenco5691 at gmail.com

SumType allows this bit of code:
```
SumType!(int, string) st;
st.match!(
  function ref int(string _) => assert(0),
  function ref int(ref int i) => i,
);
```

However, it does not allow returning a pointer to i:
```
SumType!(int, string) st;
st.match!(
  function ref int*(string _) => assert(0),
  function ref int*(ref int i) => &i,
);
```

This is because `canMatch` does not account for `ref`. The template
`valueTypes` stores all types of the member values and uses SumTypes's `get`
function, which returns a `ref`. However, ref does not persist and the type is
not sent to `canMatch` as a `ref`.

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