Codechange: Scan station catchment tiles when removing station from nearby towns/industries.

[PeterN]

Motivation / Problem

On a map with lots of towns and industries, along with lots of stations, iterating the complete town and industry pool to (possibly) remove the station from town and industry nearby stations lists can take some time.

This is most noticeable when a company goes bankrupt as lots of updates are done together, but also has a small impact on removing stations parts.

Description

Stations also have a list of catchment tiles covered, which is updated after the town and industry nearby station lists are cleared.

So we can avoid iterating all towns and industries when updating station catchment, and scan a limited portion of the map instead.

This provides a modest performance benefit when many towns/industries exist:

game	stations	towns	industries	action	before	after
reddit 1	591	512	1,560	RemoveFromAllNearbyLists() x100	2,420µs	61µs
Wentbourne	2,648	368	1,309	RemoveFromAllNearbyLists() x100	3,417µs	111µs
Xarick_4kx4k	20,856	12,538	20,873	RemoveFromAllNearbyLists() x100	823,153µs	645µs
Wentbourne				reset_company 1	499,610µs	458,537µs
Xarick_4kx4k				stop_ai 2	2,284,738µs	604,671µs

Limitations

Relies on catchment_tiles not missing any tile. It shouldn't do as that would cause other issues too.

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

[JGRennison]

Players can (and often do) bulldoze whole towns. If a town has no house tiles it wouldn't be found and the reference would be left dangling.

[PeterN]

ClearTownHouse() removes the station from Town::stations_near via RemoveNearbyStations(), so I don't think that would be affected.