feat: Allow to animate lists (in the product edition flow)

[g123k]

Hi everyone,

As part of #3986, I want to be able to animate the insertion/removal of an item.
This PR simply adds this feature, that you can see in action: AnimatedLists.webm

Edit: I've also improved a bit the accessibility with the + button

[codecov-commenter]

Codecov Report

Merging #4195 (c26a89c) into develop (38b2b8a) will decrease coverage by 0.03%.
The diff coverage is 0.00%.

@@             Coverage Diff             @@
##           develop    #4195      +/-   ##
===========================================
- Coverage    10.88%   10.86%   -0.03%     
===========================================
  Files          277      277              
  Lines        13600    13629      +29     
===========================================
  Hits          1481     1481              
- Misses       12119    12148      +29     

Impacted Files	Coverage Δ
...p/lib/pages/product/simple_input_page_helpers.dart	0.00% <0.00%> (ø)
...oth_app/lib/pages/product/simple_input_widget.dart	0.00% <0.00%> (ø)

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[teolemon]

Nice touch