[Feature] stack based plain-function-helper access to the owner during rendering

I don't want to write an RFC for this right now, as I think it'd be better to prototype the code first

during render, we always know the owner.

so when when invoking a helper (plain function or not), we could do:
```js
// internal psuedo-code
setActiveOwner() // global
invokeHelper(usersHelper) // the users helper
clearActiveOwner(); // global
```

and then
```js
function usersHelper() {
let owner = getOwner();

assert('..', owner);

let service = owner.lookup('...');

return service.format(....)
}

```

this way folks don't need to use class-based helpers or resources to get access to the owner.