Add conditional CSS class arrays to all *Class() methods

[WarLikeLaux]

Q	A
Is bugfix?	❌
New feature?	❌
Docs added?	❌
Tests added?	✔️
Breaks BC?	❌

What does this PR do?

Extends all 29 *Class() methods in Alert, Dropdown, and Menu to accept string|array. The array format supports conditional CSS classes (Laravel Blade pattern).

Menu::widget()
    ->class(['nav' => true, 'active' => $isActive, 'dark' => $isDark])
    ->activeClass(['selected' => true, 'highlight' => $isHighlighted])
    ->items($items)
    ->render();

Keys with true values are included, false are excluded. Numeric keys are always included. This replaces ternary expressions like ->class($active ? 'nav active' : 'nav').

Resolution logic is in Normalizer::cssClasses(). No BC break, existing string calls work unchanged.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (a602b53) to head (07c901d).

Additional details and impacted files

@@             Coverage Diff             @@
##              master      #143   +/-   ##
===========================================
  Coverage     100.00%   100.00%           
- Complexity       316       321    +5     
===========================================
  Files              8         8           
  Lines           1005      1015   +10     
===========================================
+ Hits            1005      1015   +10     

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[vjik]

Can we add conditional CSS class feature to Yii HTML ("class" in attributes array, Html::addCssClass() method) without BC break?