fix: Misc visual improvements

[g123k]

Hi everyone!

Here are a few visual improvements:

AppBar

• The AppBar now has a shadow by default (removed by Material 3 😵‍💫)
• The AppBar font size is a bit smaller (regression after Material 3)
   

Edit page:

• The Nutrition Facts icon is taken from the font and not the SVG (no visual change)

• The Edit icon is taken from the front (a bit rounded)

• The Country icon is taken from the front (a bit rounded)

• "Add a price" uses the same icon as in the Product page
   

• fix: Some SVGs were opting for the wrong color in dark mode
   

Misc

• CurrencySelectorHelper has a singleton

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 50.00000% with 21 lines in your changes missing coverage. Please review.

Project coverage is 7.07%. Comparing base (4d9c7fc) to head (47cedd2).
Report is 452 commits behind head on develop.

Files with missing lines	Patch %	Lines
...mooth_app/lib/pages/product/edit_product_page.dart	0.00%	15 Missing ⚠️
...lib/pages/onboarding/currency_selector_helper.dart	0.00%	3 Missing ⚠️
...ackages/smooth_app/lib/widgets/smooth_app_bar.dart	85.71%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           develop   #5829      +/-   ##
==========================================
- Coverage     9.54%   7.07%   -2.48%     
==========================================
  Files          325     413      +88     
  Lines        16411   22540    +6129     
==========================================
+ Hits          1567    1595      +28     
- Misses       14844   20945    +6101     

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[teolemon]

thanks a lot @g123k 🌊