gen_stub: Fix handling of escape sequences in generated C strings

[NattyNarwhal]

When handling sequences like this in a stub:

<?php
class Whatever {
    public static string $foobar1 = "CCC \n\r\t\v\e\f\\\$\"\101\x41\u{41} CCC";
    public static string $foobar2 = 'CCC \n\r\t\v\e\f\\\$\"\101\x41\u{41} CCC';
}

...properly generate C headers that properly escape the string. Otherwise, the differing escaping rules and differences between PHP's single and double quoted strings could lead to mangled headers.

The output of these strings after the stub has been generated:

string(22) "BEGIN 

	��\$"AAA END"
string(43) "BEGIN \n\r\t\v\e\f\\\\$\"\101\x41\u{41} END"

And the generated arginfo:

        zend_string *property_doubleQuoteEscaped_default_value_str = zend_string_init("BEGIN \n\r\t\v\x1b\f\\$\"AAA END", strlen("BEGIN \n\r\t\v\x1b\f\\$\"AAA END"), 1);
pp      ZVAL_STR(&property_doubleQuoteEscaped_default_value, property_doubleQuoteEscaped_default_value_str);
        zend_string *property_doubleQuoteEscaped_name = zend_string_init("doubleQuoteEscaped", sizeof("doubleQuoteEscaped") - 1, true);
        zend_declare_typed_property(class_entry, property_doubleQuoteEscaped_name, &property_doubleQuoteEscaped_default_value, ZEND_ACC_PUBLIC|ZEND_ACC_STATIC, NULL, (zend_type) ZEND_TYPE_INIT_MASK(MAY_BE_STRING));
        zend_string_release_ex(property_doubleQuoteEscaped_name, true);

        zval property_singleQuoteEscaped_default_value;
        zend_string *property_singleQuoteEscaped_default_value_str = zend_string_init("BEGIN \\n\\r\\t\\v\\e\\f\\\\\\\\$\\\"\\101\\x41\\u{41} END", strlen("BEGIN \\n\\r\\t\\v\\e\\f\\\\\\\\$\\\"\\101\\x41\\u{41} END"), 1);
        ZVAL_STR(&property_singleQuoteEscaped_default_value, property_singleQuoteEscaped_default_value_str);
        zend_string *property_singleQuoteEscaped_name = zend_string_init("singleQuoteEscaped", sizeof("singleQuoteEscaped") - 1, true);
        zend_declare_typed_property(class_entry, property_singleQuoteEscaped_name, &property_singleQuoteEscaped_default_value, ZEND_ACC_PUBLIC|ZEND_ACC_STATIC, NULL, (zend_type) ZEND_TYPE_INIT_MASK(MAY_BE_STRING));
        zend_string_release_ex(property_singleQuoteEscaped_name, true);

Note that the PHP escape sequence "$" will be handled in a special manner to avoid providing it to C, to avoid C compiler warnings.

Tests are included via the zend_test stub and a phpt file to ensure that the escape sequences match.

Fixes GH-22169.

[TimWolla]

I'm also unsure how best to make tests for gen_stub, so I haven't included any beyond mentioning how to test manually with this commit.

Add it to the ext/zend_test stub.

[kocsismate]

but LGTM otherwise, thank you!