Parametric mapgen part 8: Support mapgen parameters for more mapgen ids

[jbytheway]

Summary

Infrastructure "Brief description"

Purpose of change

Continuing the work of #50853. After that PR, there were five remaining things to have mapgen_value support added to them.

Describe the solution

This PR completes three of them:

• jmapgen_gaspump's fuel type
• jmapgen_monster's monster ids
• jmapgen_sealed_item's furniture id

Ancillary changes needed for this:

• Fuel type is now an itype_id rather than simply a string.
• The monster and sealed item sanity checking code had to change quite a bit.

Describe alternatives you've considered

Doing this as more or fewer PRs.

Testing

I caused the generation of at least one OMT featuring each type changed (military helipad for the gaspump, lab basement for the monster placement, farm field for the sealed_item). They all seemed to work as expected.

Additional context

Two things remain to be ported and are put off again to a future PR:

• jmapgen_item_group's item group
• jmapgen_loot's result_group

They will be the most complicated ones to deal with.