Improve fuzzy skin with modifier

[Noisyfox]

Description

Now using fuzzy skin on modifiers no longer generate extra perimeters between regions.
Currently I only completed the code for classic wall mode. Arachne still work-in-progress.

Note: the algorithm can be slow with complicated models when using multiple modifiers (clipping and reconstructing polygons with lots of points can be computational intense), though it shouldn't slow down when using only one modifier compare to the original algorithm.

Fix #2647
Fix #5560

Screenshots/Recordings/Graphs

[Noisyfox]

Currently there will be a seam when multiple modifiers with different fuzzy settings intersect:

Not sure how to fix this though.

[Noisyfox]

Somehow the modifier affects solid layers next to top/bottom layers. Weird...

Update: this issue is not caused by this PR though. This can be reproduced by adding a modifier with any option that does not affect the perimeters (such as the ironing option) on version 2.2.0beta as well.

Update 2: This issue should now be fixed with PR #6794

[SoftFever]

LGTM
Thanks

[vgdh]

Wow. This is really great!

[northcoastam]

Great addition, thank you.

[dewi-ny-je]

It would be nice if the same was done for speed modifiers: if I set a modifier to change perimeter speed for a part of an object, the modifier adds a surface (with all that comes with it, so changes of travel, lines are broken, ...) on the interface.

See this: https://3dprinting.stackexchange.com/questions/23331/how-to-change-print-speed-along-a-perimeter

Maybe check what caused the issue you solved just for fuzzy skin and solve it at the root?

[Noisyfox]

It would be nice if the same was done for speed modifiers: if I set a modifier to change perimeter speed for a part of an object, the modifier adds a surface (with all that comes with it, so changes of travel, lines are broken, ...) on the interface.

See this: https://3dprinting.stackexchange.com/questions/23331/how-to-change-print-speed-along-a-perimeter

Maybe check what caused the issue you solved just for fuzzy skin and solve it at the root?

That won't be easy, but I'll look at this when possible.

[irowboat]

While I'm not manually assigning modifiers, color painting creates them and I have no control over it; and if someone were to use beam interlocking, things get crazy as seen here: #5185 (comment)

Care to try that test case against your build?