Change: Increase house type limit to 4096.

[PeterN]

Motivation / Problem

The house limit of 512 is quite arbitrary and can be reached quite easily. There is plenty of free bits available to houses in the map array to increase this limit.

Description

Increase the house type limit to 4096, moving map storing from 9 bits of m4+m3[6] to 12 bits of m8.

This requires a savegame bump for map conversion.

Built on top of #12287 which makes HouseSpec allocation dynamic.

Limitations

Variable 0x66 stores the local id in 8 bits, so any local id higher than 0xFF will be indistinguishable from 0xFF.

Why limit to 4096? No particular reason, 65535 would also be fine, using all of m8.

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]

Looks like HouseScopeResolver variable 0x66 was written with the limit of 255 houses per NewGRF in mind, so that'll be broken :/