Add drawable for default thumbnail for Recents Go

This CL adds a drawable for the default thumbnail view and
refactors the logic to get the default icon/thumbnail/label if
null to separate methods for re-use in later CLs.

Bug: 114136250
Test: Manual; Go to icon recents
Change-Id: I511ea40ace040fc53ffc69c27149f24d69bda7b0
(cherry picked from commit 34ee30c4)