Motivation / Problem

Continuing to reduce the number of FOR_XXX macro when it's possible.

Description

FOR_ALL_TARS was a basic iteration using _tar_filelist[sd].begin() and _tar_filelist[sd].end(), so I just replaced all usage by direct range-based for loops using _tar_filelist[sd].
FOR_ALL_SEARCHPATHS was iterating all the Searchpath enum, skipping empty searchpaths. As all these searchpaths are set only once in DeterminePaths(), I think it's simpler to just store valid searchpaths once they're set, and then use this stored value directly in for loops.
FOR_ALL_ROADTRAMTYPES is a range-based for loop with direct initialisation in the macro. It's better to add a static array with the 2 values, and use that in explicit for loops.

Limitations

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 affects the save game format? (label 'savegame upgrade')
• This PR affects the GS/AI API? (label 'needs review: Script API')
  • ai_changelog.hpp, gs_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