fix(select): do not update selected property of an option element on digest with no change event
fix(select): do not update selected property of an option element on digest with no change event

The `render()` method was being invoked on every turn of the digest cycle,
which was inadvertently updating the DOM even when a `change` event had
not been triggered.

This change only calls the `render()` method when `ctrl.$render()` is called,
as part of the NgModelController` lifecycle and when the `modelValue` has
significantly changed.

Closes #8221
Closes #7715

campersau/angular.js,campersau/angular.js