fix: The nutrition page is unusable on iOS

[g123k]

Hi everyone,

On iOS, the nutrition page is pretty much unusable because we create focus nodes on every builds.
This is absolutely not necessary and creates a weird issue, preventing sometimes entering values.

Before: https://github.com/openfoodfacts/smooth-app/assets/246838/e1672ad1-7d24-41aa-9232-81e75b8168f0
After: https://github.com/openfoodfacts/smooth-app/assets/246838/be172123-46f9-4c2d-b296-79271d01c173

[codecov-commenter]

Codecov Report

Merging #4265 (9c3ede2) into develop (7487b72) will decrease coverage by 0.01%.
The diff coverage is 0.00%.

@@             Coverage Diff             @@
##           develop    #4265      +/-   ##
===========================================
- Coverage    10.81%   10.81%   -0.01%     
===========================================
  Files          287      287              
  Lines        14216    14221       +5     
===========================================
  Hits          1538     1538              
- Misses       12678    12683       +5     

Impacted Files	Coverage Δ
...h_app/lib/pages/product/nutrition_page_loaded.dart	0.00% <0.00%> (ø)

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[monsieurtanuki]

Hi @g123k!

As we're sometimes going back and forth on the matter of focus, especially when the behavior is different on iOS and android, let me suggest two things:

1. what would happen if we didn't use explicitly focus and let flutter figure out that widgets in a column should be dealt with in the same order? Would that work? Wouldn't the code be easier to maintain then?
2. if the previous suggestion fails, I strongly suggest an explicit comment like "CAUTION - LEAVE THE FOCUS AS THEY ARE - DIFFERENT BEHAVIOR ON IOS AND ANDROID"

[g123k]

Hi @g123k!

As we're sometimes going back and forth on the matter of focus, especially when the behavior is different on iOS and android, let me suggest two things:

1. what would happen if we didn't use explicitly focus and let flutter figure out that widgets in a column should be dealt with in the same order? Would that work? Wouldn't the code be easier to maintain then?
2. if the previous suggestion fails, I strongly suggest an explicit comment like "CAUTION - LEAVE THE FOCUS AS THEY ARE - DIFFERENT BEHAVIOR ON IOS AND ANDROID"

I think the issue was actually on both platforms and not only on iOS.
But keyboards are managed differently, hence the fact that's more visible on iOS.

Depending on the default behavior could work, but for accessibility, it's better to explicitly provide the next node.
So, I would let the code as-is, because the only issue we had, was the fact that FocusNodes should remain between builds.

[monsieurtanuki]

@g123k Ok then!
Was probably caused by a recent PR like #4187 (2 weeks ago) because I used the nutrition screen last month for my tests on android and didn't notice anything strange.
Thank you for the fix!

[g123k]

I forgot to merge this one, so let's do this.
And thanks @monsieurtanuki for your review!