`Array(::AbstractRange)` should return an `Array` (#50568)
Currently, `Array(r::AbstractRange)` falls back to `vcat(r)`, but
certain ranges may choose to specialize `vcat(r::AbstractRange)` to not
return an `Array`. This PR ensures that `Array(r)` always returns an
`Array`.
At present, there's some code overlap with `vcat` (just above the
`Array` method added in this PR). Perhaps some of these may be replaced
by `unsafe_copyto!`, but the tests for ranges include some special cases
that don't support `getindex`, which complicates things a bit. I've not
done this for now. In any case, the common bit of code is pretty simple,
so perhaps the duplication is harmless.
