test: add the pwtest test framework

Heavily inspired by libinput's litest framework (built around check), this is
a from-scratch framework that simplifies adding tests for various parts of
pipewire. See the pwtest.h documentation for details but the basics are:

- PW_TEST() and PWTEST_SUITE() specify the tests to be run
- Test are run in forked processes, any errors/signals are caught and printed
  to the log
- Tests have a custom pipewire daemon started on demand to talk to [1]. The
  daemon's log is available in the test output.
- Output is YAML to be processed into whatever format needed

[1] There are limits here, since we can't emulate devices yet there is only
so much we can rely on with the daemon.

meson.build

@@ -372,10 +372,19 @@ installed_tests_execdir = pipewire_libexecdir / 'installed-tests' / pipewire_nam
 installed_tests_enabled = not get_option('installed_tests').disabled()
 installed_tests_template = files('template.test.in')
 
+if not get_option('tests').disabled()
+  gstack = find_program('gstack', required : false)
+  cdata.set10('HAVE_GSTACK', gstack.found())
+endif
+
 subdir('po')
 subdir('spa')
 subdir('src')
 
+if not get_option('tests').disabled()
+  subdir('test')
+endif
+
 configure_file(input : 'config.h.meson',
   output : 'config.h',
   configuration : cdata)