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.

test/meson.build

@@ -0,0 +1,38 @@
+pwtest_sources = [
+  'pwtest.h',
+  'pwtest-implementation.h',
+  'pwtest.c',
+]
+
+pwtest_deps = [
+  pipewire_dep,
+  mathlib,
+]
+
+pwtest_c_args = [
+  '-DHAVE_CONFIG_H',
+  '-DBUILD_ROOT="@0@"'.format(meson.build_root()),
+  '-DSOURCE_ROOT="@0@"'.format(meson.source_root()),
+]
+
+pwtest_inc = [
+  spa_inc,
+  pipewire_inc,
+  configinc,
+  includes_inc,
+]
+
+pwtest_lib = static_library(
+  'pwtest',
+  pwtest_sources,
+  c_args: pwtest_c_args,
+  dependencies: pwtest_deps,
+  include_directories: pwtest_inc,
+)
+
+# Compilation only, this is the example file for how pwtest works and most
+# of its tests will fail.
+executable('test-example',
+  'test-example.c',
+  include_directories: pwtest_inc,
+  link_with: pwtest_lib)