Refactor CLI SAPI php_cli_server_client struct to use zend_string (#8522)

This is a stepping stone in converting more pairs of ``char*`` and ``size_t`` to ``zend_string*`` across the CLI SAPI.

Also amend the CLI SAPI test setup to output it's content when it crashes/errors so that one can debug ASAN/UBSAN/MSAN violations.

Drive-by MSAN fix.

Co-authored-by: Arnaud Le Blanc <[email protected]>

Author: Girgias