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.

Reviewed By: javache

Differential Revision: D58989535

fbshipit-source-id: 4ffe92d079acdf3ba24731f7f1ef1ae6eba97da5

gentest/gentest-validate.ts

@@ -19,7 +19,7 @@ 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,