Create gentest-validate script to validate test signatures (#1504)

Summary:
Pull Request resolved: https://github.com/facebook/yoga/pull/1504

I aim to consume this via a github action or workflow. Separating out the CI configuration from the actual script. We could and should maybe change this script to take in arguments for the test dirs so it is more configurable, but getting the barebones down right now.

Reviewed By: NickGerleman

Differential Revision: D51999865

fbshipit-source-id: 5792c6eec5692943518fecefc6226d784c6f0ad8

gentest/package.json

@@ -3,7 +3,8 @@
   "version": "0.0.0",
   "private": true,
   "scripts": {
-    "gentest": "node --loader=babel-register-esm ./gentest-driver.ts"
+    "gentest": "node --loader=babel-register-esm ./gentest-driver.ts",
+    "gentest-validate": "node --loader=babel-register-esm ./gentest-validate.ts"
   },
   "type": "module",
   "dependencies": {