Allow to load implicit layer from /vendor/app.

Currently when loading implicit layers from apks, NativeLoaderNamespace
doesn't allow to dlopen the binaries if they come from apks from
/vendor/app. Implicit layers ship within /vendor/app should work like
other implicit layers. This patch extracts the construction of library
paths of the implicit layers and includes those paths when
NativeLoaderNamespace is created as the part of the permitted library
paths.

Bug: b/157832445
Test: atest android.gputools.cts.CtsRootlessGpuDebugHostTest
Test: setup debug layer and use adb logcat to check vulkan loader output
Change-Id: Ie2ca989bcab890578b5aa540d07f2aee2a0182bd