* Add `toOpenArray[T](ptr UncheckedArray[T])` for clarity. `ptr array[0,T]`
for some unchecked type already works but A) `UncheckedArray` seems to be
the intended future way for this kind of access, and B) essentially all use
cases will have a `ptr` for that kind of array source and this call signature
lets callers drop the trailing `[]` corresponding to that `ptr` deref.
This PR relates to issue https://github.com/nim-lang/Nim/issues/9001 .
* Add a test for toOpenArray() for UncheckedArray[T]s.
1b3725e395