Add data-disabled to test fixtures (#1286)

Summary:
Pull Request resolved: https://github.com/facebook/yoga/pull/1286

This can be marked in fixtures to skip a test without commenting it out. We add one more usage of this.

The same functionality existed (unused) before for `experiments`, which I changed to `data-experiments`.

Formatting of JS tests changed to be closer to what Prettier would output, and to remove usage of `Yoga.UNDEFINED` which doesn't existi and just resolves to `undefined` (this is converted to NaN by the wrapper layer).

Reviewed By: yungsters

Differential Revision: D45723003

fbshipit-source-id: fedd16a248b8fe2541ab500731b58f4b01129339

gentest/gentest-cs.js

@@ -45,8 +45,11 @@ CSEmitter.prototype = Object.create(Emitter.prototype, {
     this.pushIndent();
   }},
 
-  emitTestPrologue:{value:function(name, experiments) {
+  emitTestPrologue:{value:function(name, experiments, disabled) {
     this.push('[Test]');
+    if (disabled) {
+      this.push('[Ignore]');
+    }
     this.push('public void Test_' + name + '()');
     this.push('{');
     this.pushIndent();