[ticket/11482] Implementation of advanced DEFINE tag

Implementation of advanced DEFINE tag and ENDDEFINE

PHPBB3-11482
[ticket/11482] Unit tests for advanced DEFINE

Unit tests for advanced DEFINE and ENDDEFINE

PHPBB3-11482
[ticket/11482] Use double quotes for code

Use double quotes for code to avoid excessive escaping

PHPBB3-11482
Merge remote-tracking branch 'remotes/cyberalien/ticket/11482' into develop

# By Vjacheslav Trushkin
# Via Vjacheslav Trushkin
* remotes/cyberalien/ticket/11482:
  [ticket/11482] Use double quotes for code
  [ticket/11482] Unit tests for advanced DEFINE
  [ticket/11482] Implementation of advanced DEFINE tag