Make `CamelCasedPropertiesDeep` preserve leading underscores

[simon-abbott]

Version 9.0.0 of camelcase changed the behavior to preserve leading underscores. This means that now trying to deeply camel case an object by mapping the keys through camelcase results in a different runtime output than the result of CamelCasedPropertiesDeep.

For example:

type DeeplyCamelCase<T> = CamelCasedPropertiesDeep<
  T,
  { preserveConsecutiveUppercase: true }
>;

/**
 * Deeply camelCases an object or array
 */
function deeplyCamelCase<T>(input: T): DeeplyCamelCase<T>;
function deeplyCamelCase(obj: unknown): unknown {
  if (Array.isArray(obj)) {
    return obj.map(deeplyCamelCase);
  }

  if (obj !== null && typeof obj === 'object') {
    return Object.entries(obj).reduce<Record<string, unknown>>(
      (result, [key, value]) => {
        const camelCaseKey = camelCase(key, {
          preserveConsecutiveUppercase: true,
        });
        result[camelCaseKey] = deeplyCamelCase(value);
        return result;
      },
      {},
    );
  }

  return obj;
}

const dcc = deeplyCamelCase({ _foo_bar: 'baz' });
// At this point dcc has type `{ fooBar }`, but the runtime output is `{ _fooBar }`

I think that these types should be kept in sync (or at least have an option, like preserveConsecutiveUppercase, to keep leading underscores).