fix avoid crossing peri, fix gapfill, and some others

Merge branch 'stable'

Merge branch 'stable'

add custom vars, fix min/max layer height, custom gcode unsaved change

Merge branch 'dev'

version 2.3.57.3

Merge branch 'dev'

Merge branch 'dev'

Merge branch 'merill-merge'

Fix for supermerill#888

The CallAfter() on Linux causes weird window focus issues.

For me, using ALT-Tab to switch away from PrusaSlicer/SuperSlicer would cause
PrusaSlicer/SuperSlicer to take back focus after about one second.  Stranger
things reportedly occur with focus-follows-mouse.

The #ifdef is there because it is assumed the CallAfter() was added
in 20f5b7a for a good reason.