refactor: make route() take a predicate for path_avoid

[nornagon]

Summary

None

Purpose of change

Refactor map::route for a minor performance win and to support future
simplifications and bugfixes.

Describe the solution

Before
map::route takes a set of points to "preclose", i.e. never to path through.
Whenever calling map::route, callers assemble the full "preclosed" set
containing every point to avoid.

After
map::route takes a predicate that returns whether a point should be avoided.
This allows callers to avoid the overhead of assembling the full "preclosed"
set. In cases where paths are short, this may improve performance by not
considering points outside a very small radius. In cases where paths are long,
it should still improve performance in most cases as the predicate is called
only once per point that the pathfinding algorithm considers, which may be
smaller than the full set of points to avoid. Additionally, callers no longer
have to choose a radius in which to compute points to be avoided.

In some cases this might be slower than the previous approach, specifically
because the "avoid" calculation isn't cached, and may be called up to 8 times
per tile in pathological cases (one for each direction from which the pather
could enter the tile).

This change should have no observable effect on behavior. However, in future,
I'd like to refactor again to change the predicate into a function returning a
weight, which would allow expressing the concept "avoid this point if possible,
but if it's the only way to reach the destination, it's fine".

See #71532.

Describe alternatives you've considered

Testing

Additional context

[Maleclypse]

Conflict needs resolving

[nornagon]

test failure seems unrelated.