Amphtml: amp-selector: `[selected]` attribute with `amp-bind` conflicts with manual selection

[aghassemi]

If selected attribute of amp-selector is changed view bind, and then manually via tap, the binding stops working.

I believe this is because the manual tap does not update the selected attribute so bind on the next updates does not believe it is actually changing the value and therefore does not mutate.

/cc @camelburrito

[djavet]

Full sample code here: https://codepen.io/aghassemi/pen/jaLrjR

[aghassemi]

closing in favour of https://github.com/ampproject/amphtml/issues/12058, root cause is deeper than amp-selector

[aghassemi]

worked around added to https://codepen.io/aghassemi/pen/jaLrjR