Add parser tests for animation properties

This adds tests for animation-name, animation-duration,
animation-timing-function, animation-iteration-count,
animation-direction, animation-play-state, animation-delay
and animation-fill-mode.

testsuite/css/parser/animation-timing-function.ref.css

@@ -0,0 +1,35 @@
+a {
+  animation-timing-function: initial;
+}
+
+b {
+  animation-timing-function: inherit;
+}
+
+c {
+  animation-timing-function: unset;
+}
+
+d {
+  animation-timing-function: ease;
+}
+
+e {
+  animation-timing-function: ease, linear, ease-in, ease-out, ease-in-out, step-start, step-end;
+}
+
+f {
+  animation-timing-function: cubic-bezier(0,0.25,1,2.7);
+}
+
+g {
+  animation-timing-function: steps(3);
+}
+
+h {
+  animation-timing-function: steps(5,start);
+}
+
+i {
+  animation-timing-function: steps(7);
+}