Don't use VLA's in unit tests and API examples (#3002)

MSVC doesn't support C99 VLA (variable-length array).
Use fixed size arrays in API examples and use JERRY_VLA macro
in unit tests to make these tests buildable on Windows too.

JerryScript-DCO-1.0-Signed-off-by: Csaba Osztrogonác oszi@inf.u-szeged.hu

tests/unit-core/test-regexp.c

@@ -48,7 +48,7 @@ main (void)
   jerry_value_t is_global = jerry_get_property_by_index (res, 2);
 
   jerry_size_t str_size = jerry_get_string_size (regex_res_str);
-  jerry_char_t res_buff[str_size];
+  JERRY_VLA (jerry_char_t, res_buff, str_size);
   jerry_size_t res_size = jerry_string_to_char_buffer (regex_res_str, res_buff, str_size);
 
   const char expected_result[] = "something";