Add some css parser tests

These tests exercise many allowed ways to specify various
properties.

testsuite/css/parser/text-decoration-style.css

@@ -0,0 +1,23 @@
+a {
+  text-decoration-style: initial;
+}
+
+b {
+  text-decoration-style: inherit;
+}
+
+c {
+  text-decoration-style: unset;
+}
+
+d {
+  text-decoration-style: solid;
+}
+
+e {
+  text-decoration-style: double;
+}
+
+f {
+  text-decoration-style: wavy;
+}