fix(ngOptions): throw if ngModel is not present

Closes #7047
Closes #12840

BREAKING CHANGE:
`ngOptions` will now throw if `ngModel` is not present on the `select`
element. Previously, having no `ngModel` let `ngOptions` silently
fail, which could lead to hard to debug errors. The change should
therefore not affect any applications, as it simply makes the
requirement more strict and alerts the developer explicitly.