[RFC][FIX] OWScatterPlot: Change output Feature to AttributeList

[janezd]

Issue

Fixes #2687.

Description of changes

Change the output type of Feature to AttributeList. Alternatively, input could be changed to Table but other widget (Sieve, Select columns...) use AttributeList; I see little use for Table in these contexts.

Includes

• Code changes
• Tests

[codecov-io]

Codecov Report

Merging #2689 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #2689      +/-   ##
==========================================
+ Coverage   75.82%   75.82%   +<.01%     
==========================================
  Files         338      338              
  Lines       59459    59464       +5     
==========================================
+ Hits        45082    45087       +5     
  Misses      14377    14377

[janezd]

The widget still outputs the signal Feature even when the auto send is disabled (like it did before this PR). I don't see much wrong with it: the auto send setting applies to the data, while features are just always send.

If this is undesired, let @lanzagar contribute a commit with a fix and I'll add a test, as in #2685. :)

[lanzagar]

Not sure if it is undesired. It could be a bit confusing, but is also simple enough that I don't think we need to worry about it until we hear a complaint :)

[Side Note] I am not even sure we need an auto-send control here at all. They make sense in widgets where an action could take time. When we just want to avoid updates in downstream widgets, this can be done by pausing the signal. That should probably be the preferred/universal way, and it could be up for (a future) discussion whether another way to do the same thing is good.
Just food for thought, not opening that discussion here and now.