* Fix regression in jinja2 include search path
Since commit 3c39bb5, the 'ansible_search_path' variable is used to set
jinja2's search path for {% include %} directives. However, this path is
the the proper one because our templates live in 'templates' subdirs in
our search path.
This is a regression because previously, our include search path would
include the dirname of the currently interpreted file, which worked most
of the time.
fixes#18526
* Fix template lookup search path
Improve fix in commit c96c853 so that the search path contain both
template-suffixed paths as well as original paths.
ref PR #18617
* Add integration test for template lookups
Tests regression at #18526
This test fails on current devel branch and succeeds on PR #18617
