[php-src] Issue #19523: The **const** modifier needs to be added to read-only parameters of all ZendAPI and PHPAPI functions

Issue: https://github.com/php/php-src/issues/19523 Author: matyhtf ### Description Many functions in the php source code receive the zval parameter. The value of the parameter is not modified in the function implementation. These parameters are read-only, but the const modifier is not added. As a result, C/C++underlying developers do not know whether the function is a read-only operation or a write operation, and will pollute all downstream functions. If these PHPAPI or ZEND_API functions are used in a C++function, even if the function is designed to be read-only, the const modifier cannot be used, or only unsafe const_cast can be used to cast. ## An example: ```cpp class Variant { protected: zval val; void destroy() { zval_ptr_dtor(&val); } public: Variant(const zval *v) noexcept { ZVAL_COPY_VALUE(&val, v); } const zval *const_ptr() const { return &val; } // fast_equal_check_function should be fast_equal_check_function(const zval *op1, const zval *op2) bool equals(const Variant &v) const { return fast_equal_check_function(const_ptr(), v.const_ptr()); } } ``` ## Problem function: - fast_equal_check_function - php_debug_zval_dump - php_var_dump - php_var_unserialize - concat_function - add_function - is_equal_function - zval_get_string - zval_get_double // version 8.1 ... a lot more functions