Extensions are unable to use PHPBB_USE_BOARD_URL_PATH

This PR:

https://tracker.phpbb.com/browse/PHPBB3-13276

is now breaking TONS of existing extensions under phpBB 3.3.11.
It blocks extensions from defining PHPBB_USE_BOARD_URL_PATH and hardcodes the path helper path before an extension can set the constant! The issue is due the environment.php core file initializing the web path before extensions are loaded. (see attached)

I'm not sure how the reviewer of that PR blindly approved it considering all the extensions in the wild at this point. By the way "Path" issues have been a plague since phpBB 3.1.0 launch.

Regards