Fix talkback doesn't speak subtext info

In the original design, we only set title description for
view holder, this is wrong. It causes talkback can't
speak subtext info.

Currently, we set the title content description in the title
view directly, so talkback can say the title and subtext now
when talkback focus on an app view.

Test: Talkback speaks full information for an app entry
Fix: 177873163
Change-Id: I94996d596a85cc2813ed1b10cdd4ed2bee62f4a9