Let talkback can identify a hyper link

Assign an URL span on the learn more text view,
so talkback can treat it as a hyperlink now.

Then, user can use three-fingers gesture to open
talkback menu.

Test: Set an action on a footer preference, and use talkabck.
Talkback speaks correct content and user can operate the talkback
menu.
Fix: 188009297

Change-Id: I33aa27cfa8e9eba95375eb361a5e035a803a9759