Add test support for intrinsic sized nodes

Summary: 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.

Differential Revision: D58307002

gentest/gentest-javascript.js

@@ -23,6 +23,9 @@ JavascriptEmitter.prototype = Object.create(Emitter.prototype, {
 
   emitPrologue: {
     value: function () {
+      this.push(
+        "import { instrinsicSizeMeasureFunc } from '../tools/utils.ts'",
+      );
       this.push("import Yoga from 'yoga-layout';");
       this.push('import {');
       this.pushIndent();
@@ -398,4 +401,12 @@ JavascriptEmitter.prototype = Object.create(Emitter.prototype, {
       );
     },
   },
+
+  YGNodeSetMeasureFunc: {
+    value: function (nodeName, innerText) {
+      this.push(
+        `${nodeName}.setMeasureFunc(instrinsicSizeMeasureFunc.bind("${innerText}"));`,
+      );
+    },
+  },
 });