Migration for vehicle parts that are installed in vehicles

[Soup-de-Loop]

Is your feature request related to a problem? Please describe.

In my attempts to modernise blazemod code, I initially thought that I would be able to make it save-game compatible, albeit with some extensive migration and obsoletion code. However, while items and recipes seem to be able to be redacted without too much issue, and even vehicleparts as items, vehicle parts as they exist as part of an existing vehicle in the save resist transition.

Describe the solution you'd like

If at all possible, a json form to migrate vehicle parts existent on vehicles over to another part or even the ability to have removed would be excellent for keeping saves backwards compatible when a vehicle part becomes superseded or unnecessary in its current form.

Describe alternatives you've considered

Requiring a save-compatibility break every time a vehicle part is removed or noticeably changed in the code, as it stands.

Additional context

Testing: Start a new world, mechanics 3 skill. Save game and quit, add "blazemod" entry to mods.json in the save, start up game, spawn a humvee vehicle and a TDI gun, remove the M240 from the turret and install the TDI as a blazemod turret. Save game, quit. Remove "blazemod" from mods.json, attempt to load the save, receive a seg fault which has this error in the debuglog:

ERROR : src/veh_type.cpp:589 [static void vpart_info::check()] vehicle part turretframe uses undefined item turretframe

Same error occurs with or without migration code line:

  {
    "id": "turretframe",
    "type": "MIGRATION",
    "replace": "turret"
  }

I'm not sure if being able to separately migrate items and vehicleparts would help, though in this case the turretframe item and the turretframe vehiclepart share the same id.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions. Please do not 'bump' or comment on this issue unless you are actively working on it. Stale issues, and stale issues that are closed are still considered.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions. Please do not 'bump' or comment on this issue unless you are actively working on it. Stale issues, and stale issues that are closed are still considered.

[stale]

This issue has been automatically closed due to lack of activity. This does not mean that we do not value the issue. Feel free to request that it be re-opened if you are going to actively work on it