Fix: do not use lengthof() for non C-style arrays

[rubidium42]

Motivation / Problem

Using lengthof of C++-containers is all kinds of bad.

Description

Replace the cases where lengthof was used incorrectly with a simple substitute. It's not the proper-proper fix, but that requires migrating more to proper C++-containers and that makes backporting this a lot harder.

Replace lengthof with a variant that simply causes compilation failures when a non C-style array is passed. It is the way the locations with problems were found.

Limitations

Going fully C++ containers is the better way, but baby steps.
This is just trying to do the minimum to have something that can be backported easily.

Checklist for review

Some things are not automated, and forgotten often. This list is a reminder for the reviewers.

• The bug fix is important enough to be backported? (label: 'backport requested')
• This PR touches english.txt or translations? Check the guidelines
• This PR affects the save game format? (label 'savegame upgrade')
• This PR affects the GS/AI API? (label 'needs review: Script API')
  • ai_changelog.hpp, game_changelog.hpp need updating.
  • The compatibility wrappers (compat_*.nut) need updating.
• This PR affects the NewGRF API? (label 'needs review: NewGRF')
  • newgrf_debug_data.h may need updating.
  • PR must be added to API tracker

[PeterN]

Surprisingly few, tbh.