Mark pod correctly for view sequence

[IsseW]

From what I can tell only the last pod in a view sequence was correctly marked when ChangeFlags::Paint was requested. This should mark the correct pod and not just the last one.

[Philipp-M]

Have you noticed any issues?

The elements.mark() is necessary, otherwise no tree-structure updates go through.

This code should be run per view, and elements.mark takes the current last Pod to mark changes (which should already be pod in that code).
Everytime mutate (a few lines earlier) is run, a new pod (current of the view) is added to the elements.

[IsseW]

Have you noticed any issues?

The issue I noticed was for rebuild, where the current last pod always seems to be the last pod. If it's mplemented like it is for LinearLayout. Of course I could've missed something though, still pretty new to learning about how xilem works.

This change fixes that for me at least. Where the specific problem I had was an image not changing if I only returned ChangeFlags::Paint. And found out through some debugging that the paint was being sent to the last element in the sequence.

[IsseW]

The elements.mark() is necessary, otherwise no tree-structure updates go through.

I can see this now with what TreeStructureSplice is doing. Only considered what VecSplice did earlier... But TreeStructureSplice still calls VecSplice which will only mark the last element.

[Philipp-M]

Can you check if #187 fixes the issue?

[IsseW]

Closing in favor of #187. And moving discussion there