Originally move when it was in the stdlib as _move was behind a keyword but we
moved it in front to allow for some testing. Now that we are going with a
keyword (which we can't leave in/deprecate) move it behind the move only
experimental flag until this gets through evolution.
I also updated the move function tests to show that this is working. As a nice
bonus, I was able to enable all of the tests also in a non-optimized stdlib.
We process these as loadable vars. This is really useful since it ensures that
uniqueness is preserved in this case:
```
let x: K2
do {
x = self.k2
}
switch _move(x)[userHandle] {
case .foo:
assert(_isUnique(&self.k2))
}
```
I added a test that proves this.
