allow creatures to be considered valid targets for examine highlighting

[esotericist]

Summary

SUMMARY: Bugfixes "allow creatures to be considered valid targets for examine highlighting"

Purpose of change

After #37597 it became impossible to examine tiles with creatures in them if there were no other examinables nearby, due to the examine highlighting not considering creatures valid examine targets.

Describe the solution

add a check for creatures in the can_examine_at() logic

Describe alternatives you've considered

reverting the change to examine to emit an error message if nothing to examine is nearby

it's possible to make the test more nuanced (since the examine logic has several things it checks for in determining if a creature can be interacted with), but I felt attempting to duplicate those checks would be too brittle.

Testing

loaded game, examined tamed horse, npc, etc. both with and without "autoselect if exactly one valid target" enabled