[ENH] DomainEditor: Indicate changed variables with bold face font

[janezd]

Issue

Fixes #2673 and fixes #3563.

Description of changes

Model remembers the original data and implements FontRole to return a bold font if the line was changed.

I sincerely don't know how to reasonably test this. It's all just a game of signals.

Includes

• Code changes
• Tests
• Documentation

[codecov]

Codecov Report

Merging #3576 into master will decrease coverage by <.01%.
The diff coverage is 52.38%.

@@            Coverage Diff            @@
##           master   #3576      +/-   ##
=========================================
- Coverage   84.31%   84.3%   -0.01%     
=========================================
  Files         370     370              
  Lines       67838   67858      +20     
=========================================
+ Hits        57197   57211      +14     
- Misses      10641   10647       +6

[lanzagar]

Does not work correctly for me.
After some clicking, currently it fails even just opening the File widget and changing sepal width to meta (it does not become bold), then clicking Reload makes it bold and combinations of changes with clicking Reset, Apply, Reload almost always lead to inconsistencies.
(I cleared widget settings and it still fails as early as described above, which is strange, because at first I though it was working fine, until some random clicking).

[janezd]

It's amazing that it worked for me on macOs, but indeed fails on Linux. The problem was in a list that had to be deepcopied, not just copied.

I noticed that changing a variable's position (e.g. feature -> meta) is correctly indicated with bold font, but has no effect on the output. This is an unrelated problem that already exists on master.

[janezd]

LOL, changing feature -> meta of course works. I was observing the output on Select columns, which just reversed any change -- because that's exactly what it does. :)

[ajdapretnar]

This works well for me after a short test. However, changes are indicated with italics not bold. I like it that way, but we could make it clear in the PR as well.

[janezd]

                font = QFont()
                font.setBold(True)

gives italic!? It's bold on my machine.

[ajdapretnar]

Sorry, I was being stupid. I was looking at Edit Domain, I obviously didn't read the PR title well enough. It is indeed in bold. And it works, too. I mean the one in File widget.

[markotoplak]

@janezd, I particularly like that reset button. Looks cool. :)