[PR-Reviewer] Refactor SearchView color application logic

[Copilot]

Review Feedback for PR dotnet#32187

This PR fixes Issue dotnet#25153 where SearchBar underline and search icon don't update on Android theme changes.

Assessment

Recommendation: ⚠️ Request Changes (minor)

Code Quality: Excellent refactoring following DRY principles. Eliminates duplicate icon tinting code and adds missing underline tinting.

Test Coverage: 20 visual test snapshots updated correctly.

Required Change

Update method documentation to use XML format:

// Current:
// Tints the magnifier icon and the underline
static void ApplyDecorColor(SearchView searchView, Color color)

// Should be:
/// <summary>
/// Tints the magnifier icon and the underline.
/// </summary>
static void ApplyDecorColor(SearchView searchView, Color color)

Technical Analysis

Root Cause: UpdatePlaceholderColor and UpdateTextColor only tinted magnifier icon, not the underline (search_plate background).

The Fix: New ApplyDecorColor() method tints both elements atomically:

• Magnifier icon (search_mag_icon)
• Underline (search_plate background)

Why This Works: Theme changes invoke UpdateTextColor/UpdatePlaceholderColor → ApplyDecorColor ensures both decorative elements update together.

Design Note

ApplyDecorColor only applies when using default theme colors (i.e., when PlaceholderColor or TextColor is null). Custom colors affect text only; decorative elements follow theme unless overridden via SearchIconColor property.

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Detailed review: See Review_Feedback_Issue_25153.md

Original prompt

please review dotnet#32187

Custom agent used: pr-reviewer
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