Prevent vehicles spawning inside others

[Procyonae]

Summary

None

Purpose of change

This is dumb

Having a hardcoded solution just for trying to spawn shopping carts on other vehicles (not even vice versa) is also dumb

Describe the solution

Prevent spawning vehicles if either vehicles tripoints are a subset of (or the same as) the others
Adds a unit test to check stuff is working properly

Describe alternatives you've considered

Ideally this would allow for crashes where one vehicle is a subset of the other but it still looks believable
eg

XXX
XXX
XXX

hits

...
YYY
YYY

like

XXX
ZZZ
ZZZ

But handling that without allowing other nonsense or making the check expensive seems difficult

Testing

Having some trouble with the normal intersection test, see unit test comments
Ok I'm extra confused, adding a check at the end for

a = veh_pointer_or_null( here.veh_at( tripoint_bub_ms( 61, 62, 0 ) ) );
REQUIRE( a );
if( a ) {
  CHECK( a->get_points().size() == 2 );
}

passes every time which makes it seem like it's just incorrectly returning nullptr but then if I load up the resulting test save (with the last two destroy_vehicle s commented out and tping the pc nearby) there's only 4 vehicle tiles in a square not the reported 5 in a U

Additional context

[Maleclypse]

Won’t this break car wreck extras?

[Procyonae]

No (if it was working) it doesn't prevent partially overlapping vehicles spawning

[Bone-blood-moss]

Never encountered vehicle overlap. Will break wrecks though. Picture doesn't show vehicle overlap lookes like a crash.

[Procyonae]

Never encountered vehicle overlap. Will break wrecks though. Picture doesn't show vehicle overlap lookes like a crash.

Overlapping vehicles are how you form wrecks, the screenshot is courtesy of Maarifrah pointing out this is a problem for #78382, not a crash