Update xplat/js/tools/metro Babel config to use `babel-plugin-syntax-…

…hermes-parser`

Summary:
`babel-plugin-syntax-hermes-parser` allows us to use the latest Flow syntax.

After changes to the plugin SamZ made for version 0.18.1, it only applies to Flow files (leaving TS files to be parsed by Babel): https://github.com/facebook/hermes/blob/main/tools/hermes-parser/js/CHANGELOG.md#0181

Reviewed By: robhogan

Differential Revision: D53597388

fbshipit-source-id: 461627483a6726377fbdc7a452afb808d1479b75

babel.config.js

@@ -19,6 +19,7 @@ const fs = require('fs');
 import type {BabelCoreOptions} from '@babel/core';
 */
 const plugins = [
+  'babel-plugin-syntax-hermes-parser',
   '@babel/plugin-transform-flow-strip-types',
   '@babel/plugin-transform-modules-commonjs',
   '@babel/plugin-syntax-class-properties',

package.json

@@ -10,6 +10,7 @@
     "@typescript-eslint/parser": "^6.7.4",
     "acorn": "^8.7.1",
     "babel-jest": "^29.6.3",
+    "babel-plugin-syntax-hermes-parser": "0.19.1",
     "chalk": "^4.0.0",
     "debug": "^2.2.0",
     "eslint": "^8.23.1",