Switch reflection to use smart_str

Instead of yet-another-smart-string-implementation.

Expand the smart_str API by:
 * smart_str_extract() which gets a finalized zend_string* from a
   smart_str, including insertion of the zero byte and handling of
   the empty string case. This should be preferred over using
   smart_str_0() in conjunction with str.s.
 * smart_str_get_len() which gets the length of the smart_str with
   handling of the empty string case.

Zend/zend_smart_str.h

@@ -20,6 +20,7 @@
 #define ZEND_SMART_STR_H
 
 #include <zend.h>
+#include "zend_globals.h"
 #include "zend_smart_str_public.h"
 
 #define smart_str_appends_ex(dest, src, what) \
@@ -82,6 +83,22 @@ static zend_always_inline void smart_str_0(smart_str *str) {
 	}
 }
 
+static zend_always_inline size_t smart_str_get_len(smart_str *str) {
+	return str->s ? ZSTR_LEN(str->s) : 0;
+}
+
+static zend_always_inline zend_string *smart_str_extract(smart_str *str) {
+	if (str->s) {
+		zend_string *res;
+		smart_str_0(str);
+		res = str->s;
+		str->s = NULL;
+		return res;
+	} else {
+		return ZSTR_EMPTY_ALLOC();
+	}
+}
+
 static zend_always_inline void smart_str_appendc_ex(smart_str *dest, char ch, zend_bool persistent) {
 	size_t new_len = smart_str_alloc(dest, 1, persistent);
 	ZSTR_VAL(dest->s)[new_len - 1] = ch;