Add test support for intrinsic sized nodes (#1671)

Summary:
Pull Request resolved: https://github.com/facebook/yoga/pull/1671

This diff adds support for intrinsic sizing in generated tests. This is done by importing a testing font called "Ahem" which, as used, has an exact width and height of 10px for each character. Support has been added for C++, Java, and Javascript generated tests.

Reviewed By: NickGerleman

Differential Revision: D58307002

fbshipit-source-id: e1dcc1e03310d35a32e0c70f71994880d8f7de55

gentest/gentest-cpp.js

@@ -30,7 +30,12 @@ CPPEmitter.prototype = Object.create(Emitter.prototype, {
 
   emitPrologue: {
     value: function () {
-      this.push(['#include <gtest/gtest.h>', '#include <yoga/Yoga.h>', '']);
+      this.push([
+        '#include <gtest/gtest.h>',
+        '#include <yoga/Yoga.h>',
+        '#include "../util/TestUtil.h"',
+        '',
+      ]);
     },
   },
 
@@ -503,4 +508,13 @@ CPPEmitter.prototype = Object.create(Emitter.prototype, {
       );
     },
   },
+
+  YGNodeSetMeasureFunc: {
+    value: function (nodeName, innerText) {
+      this.push(`YGNodeSetContext(${nodeName}, (void*)"${innerText}");`);
+      this.push(
+        `YGNodeSetMeasureFunc(${nodeName}, &facebook::yoga::test::IntrinsicSizeMeasure);`,
+      );
+    },
+  },
 });