Add some css parser tests

These tests exercise many allowed ways to specify various
properties.

testsuite/css/parser/font-stretch.ref.css

@@ -0,0 +1,47 @@
+a {
+  font-stretch: initial;
+}
+
+b {
+  font-stretch: inherit;
+}
+
+c {
+  font-stretch: unset;
+}
+
+d {
+  font-stretch: ultra-condensed;
+}
+
+e {
+  font-stretch: extra-condensed;
+}
+
+f {
+  font-stretch: condensed;
+}
+
+g {
+  font-stretch: semi-condensed;
+}
+
+h {
+  font-stretch: normal;
+}
+
+i {
+  font-stretch: semi-expanded;
+}
+
+j {
+  font-stretch: expanded;
+}
+
+k {
+  font-stretch: extra-expanded;
+}
+
+l {
+  font-stretch: ultra-expanded;
+}