fix(ulp): use builtin v2 project for legacy embed

Route ulp_embed_binary() through a built-in CMake v2 default ULP project instead of generating a compatibility project with a synthetic main component.

Attach legacy ULP sources directly to the ULP executable, pass the parent component include view through the existing ULP_S_SOURCES/COMPONENT_* channel, and remove the generated legacy project templates plus the component path ownership validation bypass they required.

Update the build-system coverage to assert that the builtin child project builds and rebuilds when parent-owned ULP sources change.

tools/cmakev2/component_validation.cmake

@@ -170,11 +170,6 @@ function(__component_validation_run_checks)
 
     # Run validation checks for each component
     foreach(component_interface ${component_interfaces})
-        __idf_component_get_property_unchecked(skip_path_ownership_validation ${component_interface}
-                                               __SKIP_COMPONENT_PATH_OWNERSHIP_VALIDATION)
-        if(skip_path_ownership_validation)
-            continue()
-        endif()
         __component_validation_check_sources(${component_interface})
         __component_validation_check_include_dirs(${component_interface})
     endforeach()