Use more accurate help text for z-level option

[wapcaplet]

Summary

SUMMARY: Interface "Use more accurate help text for z-level option"

Purpose of change

The so-called "Experimental z-level" option is no longer considered experimental by several other developers, and the option has never included an explanation of what it is supposed to mean, so I thought it was high time it was correctly documented in the game options menu.

Describe the solution

Changes the option label to "Z-levels" and help text to explain what it means, to make it explicit that important gameplay features require it, and to recommend against toggling it in mid-game.

Describe alternatives you've considered

None

Testing

Checked options menu for correct display and help text.

Additional context

I almost never play with this option on and had no idea so many features required it, so I can only imagine what the average player thinks.