Docs for widgets

[jpnurmi]

Added missing docs for:

• DropdownBuilder
• MenuButtonBuilder
• LocalizedView
• OptionCard

I didn't bother with AffinityExpansionTile because it's going to be replaced by ExpansionTile.controlAffinity.

[codecov]

Codecov Report

Merging #140 (b93fe0c) into main (ecda535) will not change coverage.
The diff coverage is 100.00%.

❗ Current head b93fe0c differs from pull request most recent head 8f76ddd. Consider uploading reports for the commit 8f76ddd to get more accurate results

@@           Coverage Diff           @@
##             main     #140   +/-   ##
=======================================
  Coverage   70.87%   70.87%           
=======================================
  Files          27       27           
  Lines        1102     1102           
=======================================
  Hits          781      781           
  Misses        321      321           

Impacted Files	Coverage Δ
...esktop_installer/lib/widgets/dropdown_builder.dart	100.00% <ø> (ø)
..._desktop_installer/lib/widgets/localized_view.dart	100.00% <ø> (ø)
...top_installer/lib/widgets/menu_button_builder.dart	100.00% <ø> (ø)
...ntu_desktop_installer/lib/widgets/option_card.dart	100.00% <100.00%> (ø)

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[oSoMoN]

LGTM, thanks!