Add support for loading layers from the apk.

Added the vulkan_layer_path interface which is used to set the path from
ThreadedRenderer. The vulkan loader then uses this path to search for layer
libraries that come preinstalled with the app.

Change-Id: Iee7d56c1950296ba5ece3a119741406d705479a8
(cherry picked from commit 1f920c1e52bbd59405761e5403def5dbc22e331b)