Make ValuePreference not clickable by default

Explicitly set itemView.isClickable to false for ValuePreference.
Additionally, only set OnClickListener on the value containers if
onValueClickListener is not null, preventing them from becoming
clickable when no action is defined.

Bug: 435609855
Test: manual test with sample app
Flag: EXEMPT bugfix
Change-Id: I7df7af5bb865959668a0c9789120a085c798d9a1