Talkback: handle link taps

[processprocess]

Currently, activating a link with TalkBack will trigger a page advancement.

Expected behavior from TalkBack would be to open the link.

This is where navigation or tooltip logic starts and may be a starting point for fixing this: https://github.com/ampproject/amphtml/blob/2cb692aeb7bbd2a7c3430902625b0becdc2e0172/extensions/amp-story/1.0/page-advancement.js#L623

cc @ampproject/wg-stories b/167730141

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