Describe the bug
dplx_target_sources() tries to find source files in the include directory if SMART_SOURCE is requested without MERGED_LAYOUT.
Expected behavior
Given the dplx_target_sources() invocation above the headers should be referenced within the include directory while (test) TUs should be referenced within the src directory.
Environment
Additional context
The dplx_target_sources function could profit from using target_sources(FILE_SET for installing public header files