testsuite: Add render test for texture placement

Make sure that texture nodes sample from the texture properly.

testsuite/gsk/compare/texture-coords.node

@@ -0,0 +1,9 @@
+color-matrix {
+  matrix: matrix3d(1000, 0, 0, 0, 0, 1000, 0, 0, 0, 0, 1000, 0, 0, 0, 0, 1000);
+  child: texture {
+    bounds: 0 0 32 32;
+    texture: url("data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAIAAAACCAYAAABytg0kAAAAFklEQVQImQXBAQEAAACAEP9PFyIK\
+FQ1Dzgf5P3fNsQAAAABJRU5ErkJggg==\
+");
+  }
+}

testsuite/gsk/meson.build

@@ -100,6 +100,7 @@ compare_render_tests = [
   'shadow-opacity',
   'shrink-rounded-border',
   'stroke',
+  'texture-coords',
   'texture-scale-filters-3d',
   'texture-scale-magnify-10000x',
   'texture-scale-magnify-rotate',