Add gsk vulkan tests

Add a testsuite called gsk-compare-vulkan to run
the gsk renderer tests with the Vulkan renderer.

The current stats:

Ok:                 184
Expected Fail:      0
Fail:               204
Unexpected Pass:    0
Skipped:            2
Timeout:            0

For now, we mark all the tests as failing to
avoid ci breakage. To run the tests locally,
you can do:

meson test -C_build --suite gsk-compare-vulkan

testsuite/gsk/meson.build

@@ -101,6 +101,7 @@ informative_render_tests = [
 
 renderers = [
   { 'name': 'gl' },
+  { 'name': 'vulkan' },
   { 'name': 'broadway', 'exclude_term': '-3d' },
   { 'name': 'cairo', 'exclude_term': '-3d' },
 ]
@@ -131,7 +132,7 @@ foreach renderer : renderers
       'gsk-compare-' + renderer_name,
     ]
 
-    if compare_xfails.contains(testname)
+    if compare_xfails.contains(testname) or renderer_name == 'vulkan'
       suites += 'failing'
     endif
 
@@ -140,7 +141,8 @@ foreach renderer : renderers
     endif
 
     if ((exclude_term == '' or not testname.contains(exclude_term)) and
-        (renderer_name != 'broadway' or broadway_enabled))
+        (renderer_name != 'broadway' or broadway_enabled) and
+        (renderer_name != 'vulkan' or have_vulkan))
       test(renderer_name + ' ' + testname, compare_render,
         args: [
           '--output', join_paths(meson.current_build_dir(), 'compare', renderer_name),