Fix GH-8364: msgfmt_format $values may not support references

We need to deref any references passed in the `$values` array. While
we could handle this in the type switch, doing it righ

Fix GH-8364: msgfmt_format $values may not support references

We need to deref any references passed in the `$values` array. While
we could handle this in the type switch, doing it right away in the
foreach loop makes that more explicit, and also circumvents the missing
range checks for integers which are not passed as int or double.

Closes GH-8407.

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