Align parsing of custom resolver options, rename arg (#42392)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/42392

Follow-up to https://github.com/facebook/react-native/pull/42333 following internal feedback. We are now aligning this to match the [`metro build` command](https://github.com/facebook/metro/blob/702e1b8fc7ab8b973bcd53f1a41f7e797cbf7dca/packages/metro/src/commands/build.js#L85-L91). This also improves validation on parsing (done after initial `commander` arg parsing as variadic string).

Changelog: [Internal]
(same as https://github.com/facebook/react-native/pull/42333)

Reviewed By: motiz88

Differential Revision: D52911017

fbshipit-source-id: 54049aa20c9db344a0f485fddf62fb267e672376

packages/community-cli-plugin/src/utils/parseKeyValueParamArray.js

@@ -0,0 +1,30 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @flow strict-local
+ * @format
+ * @oncall react_native
+ */
+
+import querystring from 'querystring';
+
+export default function parseKeyValueParamArray(
+  keyValueArray: $ReadOnlyArray<string>,
+): Record<string, string> {
+  const result = {};
+
+  for (const item of keyValueArray) {
+    if (item.indexOf('=') === -1) {
+      throw new Error('Expected parameter to include "=" but found: ' + item);
+    }
+    if (item.indexOf('&') !== -1) {
+      throw new Error('Parameter cannot include "&" but found: ' + item);
+    }
+    Object.assign(result, querystring.parse(item));
+  }
+
+  return result;
+}