Fix characters at the wrong level

[PatrikLundell]

Summary

None

Purpose of change

Fix #75424, fix #75428, i.e. map rotation moving characters to map's "official" (abs_pos) Z level rather than retaining them at their current level.
This might also deal with #75244, but since I was unable to repeat that when following the bug report instructions I can't verify that.

Describe the solution

Use the correct Z level reference when rotating maps, i.e. retain them at their current level.

Describe alternatives you've considered

Testing

Repeating the error situations for the two fixed reports and verifying that the characters showed up at the correct Z level (Van whatever at the ground level, Luliya at her usual spot at level 2, and Rubik at his trading station at level 1).

Additional context

This being caused by rotation made it hard to track down, as reproduction attempts happened to be performed on unrotated maps...