Enable Ironing on Support Layer Interface/Ceiling

[double0jimb0]

Application version
Cura 4.4.1

Platform
Windows 10 Pro

Printer
Ultimaker S5

Reproduction steps

1. "Ironing" enabled on Support Layer, "Support Layer Interaface" enabled. No ironing present in preview or as-run on machine.
2. Attempted changing all number of "top/bottom" thickness, layer #, pattern, no affect. Ironing not present on support material

Screenshot(s)
Screenshot showing the lack of ironing on Support Layer Interface/Ceiling:
https://www.dropbox.com/s/9hwgcbk6nudqniw/No%20Ironing%20at%20Support%20Interface.png?dl=0

Actual results
Without ironing, the "floor" of the Extruder 1 material seeps into the gaps of the support layer, leading. This results in inaccurate z-thickess thickess of the Extruder 1 material. Photo here showing the concentric roof pattern of the support material interface/ceiling:
https://www.dropbox.com/s/2qxc4jyz8n5ytck/Layer%20pattern%20visible%20on%20next%20layer.jpg?dl=0

Expected results
I would expect the top layer of support ceiling to be ironed to eliminate this "seeping".

Project file
https://www.dropbox.com/s/7la8lmdk8sjqk5h/UMS5_Geo%20Test.3mf?dl=0

Log file
I am not able to locate this snippet.

Additional information
None
![No Ironing at Support Interface](https://user-images.githubusercontent.com/60161317/72852717-ac1df380-3c6c-11ea-83af-cfd8a482fdfe.p

[rachael7]

Adding another vote for this. When using soluble support, with a zero Z gap, the texture of the support interface surface becomes critical to getting a good surface finish on the supported material. One of the benefits of soluble support is that with no Z gap, you get more accurate and aesthetically pleasing supported areas, but the inability to iron the top of the support interface limits that benefit. If it is implemented, it would probably need to come with a "minimum interface area for ironing" setting, so that we could prevent it from trying to iron very small support areas, like the top of towers. Thank you for your consideration.