* Add __serialize and __unserialize methods to Serializable classes
These methods will be used on PHP 7.4+ when available. Implementing them is required to suppress a deprecation notice on PHP 8.1+.
This commit also renames is_debug parameter for get_properties_hash utility functions (and related macros) to more accurately reflect its purpose of allocating a new HashTable instead of using an internal props table.
* Explicitly handle serialize output in php_phongo_cursorid_get_properties_hash
* Explicitly handle serialize output in php_phongo_writeconcern_get_properties_hash
* Note maxStalenessSeconds handling in php_phongo_readpreference_get_properties_hash
* CursorId should always serialize id as string
