gsk: Add a render test for mask modes

testsuite/gsk/compare/mask-modes.node

@@ -0,0 +1,47 @@
+mask {
+  mode: alpha;
+  source: color {
+    bounds: 0 0 30 30;
+    color: red;
+  }
+  mask: color {
+    bounds: 15 15 30 30;
+    color: white;
+  }
+}
+
+mask {
+  mode: inverted-alpha;
+  source: color {
+    bounds: 50 0 30 30;
+    color: lime;
+  }
+  mask: color {
+    bounds: 65 15 30 30;
+    color: white;
+  }
+}
+
+mask {
+  mode: luminance;
+  source: color {
+    bounds: 0 50 30 30;
+    color: yellow;
+  }
+  mask: color {
+    bounds: 15 65 30 30;
+    color: white;
+  }
+}
+
+mask {
+  mode: inverted-luminance;
+  source: color {
+    bounds: 50 50 30 30;
+    color: blue;
+  }
+  mask: color {
+    bounds: 65 65 30 30;
+    color: white;
+  }
+}

testsuite/gsk/meson.build

@@ -56,6 +56,7 @@ compare_render_tests = [
   'invalid-transform',
   'issue-3615',
   'mask',
+  'mask-modes',
   'nested-rounded-clips',
   'opacity_clip',
   'opacity-overdraw',