[ListItem] Exposing onTouchTap API in order to address Issue #6938

[max-b]

Allows for the fixing of #6938

From the conversation on #6907 it was suggested that instead of just calling an event.preventDefault within the listItem, the onTouchTap API be exposed to the user. That way it can be handled as appropriate.

• PR has tests / docs demo, and is linted.
• Commit and PR titles begin with [ComponentName], and are in imperative form: "[Component] Fix leaky abstraction".
• Description explains the issue / use-case resolved, and auto-closes the related issue(s) (http://tr.im/vFqem).

[oliviertassinari]

@max-b Thanks. Could you update the issue with your fix? I think that we could close it then.

[max-b]

@oliviertassinari done :)