[ticket/12487] Use new `microtime()` parameter
[ticket/12487] Remove legacy code

https://tracker.phpbb.com/browse/PHPBB3-12487

PHPBB3-12487
[ticket/12487] Remove inline declaration

https://tracker.phpbb.com/browse/PHPBB3-12487

PHPBB3-12487
[ticket/12487] Restore timezone comment in includes/startup.php

https://tracker.phpbb.com/browse/PHPBB3-12487

PHPBB3-12487
[ticket/12487] Remove unneeded constant definition

https://tracker.phpbb.com/browse/PHPBB3-12487

PHPBB3-12487
[ticket/12687] Add a constant to display the load time without DEBUG

PHPBB3-12687
[ticket/12687] Display the explain link only when DEBUG is set

PHPBB3-12687
[ticket/12687] Rename DISPLAY_LOAD_TIME to PHPBB_DISPLAY_LOAD_TIME

PHPBB3-12687
[ticket/12687] Return a string and move the displaying of the sql report

PHPBB3-12687
[ticket/12687] Remove globals

PHPBB3-12687
[ticket/12687] Use microtime(true)

PHPBB3-12687
[ticket/12687] Update doc block

PHPBB3-12687
[ticket/12697] Delete cached extension schema.json files after testing

PHPBB3-12697
[ticket/12687] Fix the namespace of $request

PHPBB3-12687
[ticket/12487] Use new `microtime()` parameter
[ticket/12687] Wrap $GLOBALS['starttime'] in a if

PHPBB3-12687
[ticket/12687] Don't check if memory_get_peak_usage() exists

PHPBB3-12687
[ticket/12687] Display the number of cached queries

PHPBB3-12687
[ticket/12687] Remove french spaces

PHPBB3-12687
[ticket/12487] Update code

- Replace $user->lang[] calls with $user->lang()
- Remove unused global definitions
- Remove unused variables
- Update $user->img() calls