css: Queue resize for properties that affect clip

This fixes shadows that are animated not updating the clip of the widget
they are drawn on. An example of this are the buttons in the CSS shadows
example in gtk-demo.

Reftest included

testsuite/reftests/label-text-shadow-changes-modify-clip.css

@@ -0,0 +1,19 @@
+@import "reset-to-defaults.css";
+
+@keyframes foo {
+  0% { text-shadow: 20px 20px tomato; }
+  100% { text-shadow: 20px 20px tomato; }
+}
+
+GtkLabel {
+  font-size: 40px;
+  animation-name: foo;
+  animation-duration: 100s;
+  animation-timing-function: linear;
+  animation-delay: 1ms;
+}
+
+#reference {
+  animation: initial;
+  text-shadow: 20px 20px tomato;
+}