Add optional message to display when choosing map point

[sparr]

Summary

Interface "Replace popups with informative message when choosing point(s) on the map"

Purpose of change

Currently many operations that ask the player to choose one or more points on the map either have one or more popups before/between map views, or provide no feedback at all for the purpose of the choice.

Describe the solution

Made om_target_tile and choose_point optionally show a message to the user while choosing, replaced most relevant popups with this functionality, added messages to some other cases, and moved part of one verbose popup's contents to a mission description.

Describe alternatives you've considered

Testing

I've been playing with a superset of this change for a week now.

Additional context

This is the second in a series of PRs being broken out from #77397