Update clang-format

[lmoureaux]

Is your feature request related to a problem? Please describe.
clang-format-11 is no longer shipped by Ubuntu 24.04.

Describe the solution you'd like
Upgrade to 18.

Describe alternatives you've considered

• Upgrade to an intermediate version
• Upgrade to the latest version (19)

Additional context
The diff of 18 with respect to 11 isn't very large:

 ai/default/daimilitary.h         |  2 +-
 client/views/view_map_common.cpp |  4 ++--
 common/aicore/path_finding.cpp   |  2 +-
 common/clientutils.cpp           |  2 +-
 common/events.cpp                |  2 +-
 common/featured_text.h           |  2 +-
 common/game.h                    |  2 +-
 common/helpdata.cpp              |  2 +-
 common/map.h                     | 10 +++++-----
 common/path_finder.cpp           |  2 +-
 common/requirements.cpp          |  7 ++++---
 common/server_settings.h         |  2 +-
 server/advisors/autosettlers.cpp |  2 +-
 server/aiiface.cpp               |  2 +-
 server/diplomats.cpp             |  6 ++----
 server/savegame/savecompat.cpp   |  2 +-
 server/score.cpp                 |  2 +-
 server/techtools.cpp             |  9 +++++----
 tools/ruledit/tab_enablers.cpp   |  4 ++--
 utility/bitvector.h              |  4 ++--
 utility/log.h                    | 12 ++++++------
 utility/registry_ini.h           | 84 ++++++++++++++++++++++++++++++++++++++++++------------------------------------------
 utility/shared.h                 | 14 +++++++-------
 utility/speclist.h               | 55 +++++++++++++++++++++++++++++--------------------------
 utility/specpq.h                 |  4 ++--
 utility/specvec.h                |  2 +-
 utility/support.h                |  6 +++---
 27 files changed, 125 insertions(+), 122 deletions(-)

I like most of the changes.