Docs: Add never return types to functions that always terminate.
Documents @return never on 30 functions and methods whose every control-flow path ends in exit, die(), wp_die(), or wp_send_json_*(), so static analysis knows the code following a call to them is unreachable. Native never requires PHP 8.1, so these are PHPDoc-only.
Where terminating depends on a parameter, a conditional @phpstan-return describes each case rather than over-widening to the union of both. The seven wp_die() handlers gain the same conditional wp_die() itself already carries. trackback_response() and wp_protect_special_option() never return for the parameter values that die, while redirect_canonical(), check_admin_referer(), check_ajax_referer(), and get_cli_args() narrow their return types accordingly.
The bottom type never was also incorrectly declared in the return type union for get_cli_args(), so it was removed.
Developed as subset of https://github.com/WordPress/wordpress-develop/pull/12488.
Follow-up to r62703, r62178, r62177.
Props westonruter, mukesh27.
See #64896, #64898.
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