tests/functional: Prepare the meson build system for the functional tests

tests/functional: Prepare the meson build system for the functional tests

Provide a meson.build file for the upcoming python-based functional
tests, and add some wrapper glue targets to the tests/Makefile.include
file. We are going to use two "speed" modes for the functional tests:
The "quick" tests can be run at any time (i.e. also during "make check"),
while the "thorough" tests should only be run when running a
"make check-functional" test run (since these tests might download
additional assets from the internet).

The changes to the meson.build files are partly based on an earlier
patch by Ani Sinha.

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Tested-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-ID: <20240830133841.142644-12-thuth@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>