app: do not make line art bucket fill a GimpSelectCriterion anymore.
This was my initial choice, but the more I think about it, the less I am sure this was the right choice. There was some common code (as I was making a common composite bucket fill once the line art was generated), but there is also a lot of different code and the functions were filled of exception when we were doing a line art fill. Also though there is a bit of color works (the way we decide whether a pixel is part of a stroke or not, though currently this is basic grayscale threshold), this is really not the same as other criterions. In particular this was made obvious on the Select by Color tool where the line art criterion was completely meaningless and would have had to be opted-out! This commit split a bit the code. Instead of finding the line art in the criterion list, I add a third choice to the "Fill whole selection"/"Fill similar colors" radio. In turn I create a new GimpBucketFillArea type with the 3 choices, and remove line art value from GimpSelectCriterion. I am not fully happy yet of this code, as it creates a bit of duplicate code, and I would appreciate to move some code away from gimpdrawable-* and gimppickable-* files. This may happen later. I break the work in pieces to not get too messy. Also this removes access to the smart colorization from the API, but that's probably ok as I prefer to not freeze options too early in the process since API needs to be stable. Probably we should get a concept of experimental API.
Showing with 622 additions and 376 deletions