Put generated Java tests in a "generated" folder (#1673)

Summary:
Pull Request resolved: https://github.com/facebook/yoga/pull/1673

Separate the generated Java tests from the non-generated ones, like all the other tests.

Differential Revision: D58989535

gentest/gentest-driver.ts

@@ -106,7 +106,7 @@ for (const fileName of fixtures) {
   );
 
   await fs.writeFile(
-    `${yogaDir}/java/tests/com/facebook/yoga/${fileNameNoExtension}.java`,
+    `${yogaDir}/java/tests/generated/com/facebook/yoga/${fileNameNoExtension}.java`,
     addSignatureToSourceCode(
       JSON.parse(logs[1].message.replace(/^[^"]*/, '')).replace(
         'YogaTest',

gentest/gentest-validate.ts

@@ -23,7 +23,7 @@ const filesToValidate = await glob(
   [
     'tests/generated/**/*.{h,cpp}',
     'javascript/tests/generated/**/*.test.ts',
-    'java/tests/com/facebook/yoga/**/*.java',
+    'java/tests/generated/com/facebook/yoga/**/*.java',
   ],
   {
     cwd: yogaRootDir,