less aggressive stubs refactor

Author: Girgias

ext/standard/basic_functions.stub.php

@@ -581,7 +581,7 @@ function str_ends_with(string $haystack, string $needle): bool {}
 
 function chunk_split(string $str, int $chunklen = 76, string $ending = "\r\n"): string {}
 
-function substr(string $str, int $start, ?int $length = null): string {}
+function substr(string $str, int $start, ?int $length = null): string|false {}
 
 /**
  * @param mixed $start

ext/standard/basic_functions_arginfo.h

@@ -931,7 +931,7 @@ ZEND_BEGIN_ARG_WITH_RETURN_TYPE_INFO_EX(arginfo_chunk_split, 0, 1, IS_STRING, 0)
 	ZEND_ARG_TYPE_INFO_WITH_DEFAULT_VALUE(0, ending, IS_STRING, 0, "\"\\r\\n\"")
 ZEND_END_ARG_INFO()
 
-ZEND_BEGIN_ARG_WITH_RETURN_TYPE_INFO_EX(arginfo_substr, 0, 2, IS_STRING, 0)
+ZEND_BEGIN_ARG_WITH_RETURN_TYPE_MASK_EX(arginfo_substr, 0, 2, MAY_BE_STRING|MAY_BE_FALSE)
 	ZEND_ARG_TYPE_INFO(0, str, IS_STRING, 0)
 	ZEND_ARG_TYPE_INFO(0, start, IS_LONG, 0)
 	ZEND_ARG_TYPE_INFO_WITH_DEFAULT_VALUE(0, length, IS_LONG, 1, "null")