The **const** modifier needs to be added to read-only parameters of all ZendAPI and PHPAPI functions

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:

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

Start by locating the PHPAPI and ZEND_API declarations and implementations for fast_equal_check_function, php_debug_zval_dump, php_var_dump, php_var_unserialize, concat_function, add_function, is_equal_function, zval_get_string, and zval_get_double. Determine which zval parameters are not modified, then update the applicable signatures consistently across the affected functions and verify that the PHP source still builds.