Closes #8599

Motivation / Problem

On Debian-based distributions, the executable should go to <prefix>/games, not <prefix>/bin.
Before switching to CMake, our old configure used to default to <prefix>/games.
Our CMake script uses GNUInstallDirs, which defaults to <prefix>/bin

Description

I restored games as default install bin dir, like it was in configure. We already set default data dir to share/games anyway.

Limitations

Package maintainers will need to set CMAKE_INSTALL_BINDIR if default doesn't match their target OS, but they are already used to do similar with the old configure.

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