CRM_Core_Error::formatFooException - Don't bomb on 'Error'

CRM_Core_Error::formatFooException - Don't bomb on 'Error'

PHP 7 updated the class hierarchy for exceptions. The top-level types for exceptions are now:

* class Throwable
* class Error extends Throwable
* class Exception extends Throwable

This patch fixes a problem when logging `Error`s, as in

```php
Civi::log()->warning('There was a problem', [
  'exception' => $e
]);
```

Before
------

If `$e` is an `Error`, it fails to log.

After
-----

It works whether `$e` is an `Error` or `Exception`.

See also: https://www.php.net/manual/en/language.errors.php7.php