Implicit namespace resolver allows handling of sample data

Predefined sample data uses "tools" namespace which is implicitely
defined for non-namespaced projects.
Also this makes sure Resources_Delegate.getLayout does not return null,
as it is annotated @NonNull in the framework, and improves on the error
message.

Bug: 79650937
Test: layoutlib tests
Change-Id: Id8c3b152e378444752d61c1560a2485af6d33248
(cherry picked from commit 158737b8cddc00efc84e483892ad47026637e99e)