Avoid more perimeters edition

PrusaSlicer 2.4 is out. The change will be merged into the next version.
This release contains more fixes to further stabilize the current branch.

changes

• Custom macro variables: two new keywords: 'exists' and 'default', to be able to fallback when using custom variables defined in filament & print settings.
  • 'default(var_name,value)' check if the variable exist and affect it the value if not.
    The variable can be boolean 'true' 'false', int '0' '12', double '1.0' '42.24' or string '"a string"'.
  • 'exists(var_name)' return true if present. It also creates a dummy boolean variable if not already set.
    Note that if you're using the variable in a formula, it may crash even if guarded by a {if} as everything is interpreted (no lazy check).
    So be sure to add a 'default' so it gets the right type and the formula can be interpreted (unless you just print it, in this case an 'exists' is enough).
    Using 'default' doesn't change the return value of 'exists'.
• Add a new setting 'wipe_only_crossing' to diable/enable wipe when you're using 'avoid perimeter crossing'.

fixes

• Fix 'avoid crossing perimeters' when wipe enabled. #1069
• When 'wipe on retract' on an external perimeter, continue to wipe inside the object instead of coming back to the middle of the perimeter. #2061
• profile update: Fix extrusion_spacing for Anycubic #2084
• Fix medial axis creating points on top of each other. #2099 #2102
• Some tooltip updates (thank you @blex-max for the help) #2097
• Updated ConfigManipulation (disabled/enabled) for width & spacing.
• Fix 'merge thin walls with perimeter' (unneeded travels) #2092
• 0 extrusion_spacing will always create 0-auto-extrusion_width. #2084
• fix fan kickstart reverting when it shouldn't #2076
• Fix Concentric (Filled) infill: honour gap_fill_min_area #2052
• perimeter_round_corners: disabled for the first perimeter #2046
• fix div/0 in libnest2D #2053

note: I haven't tested the linux & macos build.
For the macos-arm, you need to install it and then use xattr -cr /Applications/SuperSlicer.app. And the arm compile is still a bit buggy, creating some nan/inf somewhere.
You can have daily builds in the action menu of github.
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