Make it easier to see and manipulate the value and demos

[kylecordes]

It would be better if the demo screens would directly bind the control value into a form input, so when experimenting we could just type in a different value, this would replace the current demo mechanism where you type of value and then click "set".

However, this runs directly into an Angular bug:

angular/angular#13792

The essence of this bug is that value changes from one form control do not propagate into another form control pointing to the same FormControl object with reactive forms. This is a frustrating bug, I hope it gets fixed soon.