[Android] Fix OnIdiom threading issue by removing using statements in DeviceInfo

[Copilot]

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Description

This PR fixes a NotImplementedException that occurs when multiple threads access OnIdiom simultaneously on Android devices. The issue was reported on Galaxy XCover 5 with Android 14 but could affect any Android device under concurrent access scenarios.

Root Cause

The problem occurred in DeviceInfoImplementation.Idiom getter where using statements were used with Java objects:

// Line 44 - UiModeManager with using statement
using var uiModeManager = UiModeManager.FromContext(Application.Context);

// Line 69 - DisplayMetrics with using statement  
using var metrics = Application.Context.Resources?.DisplayMetrics;

When multiple threads access OnIdiom simultaneously:

1. Thread A calls DeviceInfo.Idiom and creates these objects with automatic disposal
2. Thread B calls DeviceInfo.Idiom and gets the same Java object instances
3. Thread A completes and disposes the objects via using
4. Thread B tries to access already-disposed objects → NotImplementedException: Do not know how to dispose: Invalid

Solution

Removed the using keyword from both problematic lines to prevent automatic disposal:

// Fixed - no automatic disposal
var uiModeManager = UiModeManager.FromContext(Application.Context);
var metrics = Application.Context.Resources?.DisplayMetrics;

This eliminates the race condition while allowing normal garbage collection when objects go out of scope.

Verification

• ✅ All existing OnIdiom tests pass (13 tests)
• ✅ Builds successfully across Android projects
• ✅ Code formatted according to repository standards
• ✅ Minimal, surgical change addressing exactly the identified issue

The fix prevents double-disposal of Java interop objects that caused the threading race condition, resolving the crash when multiple threads access OnIdiom concurrently.

Fixes #29853.

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[jonathanpeppers]

This is worth a try, because the using statements in here weren't helping cross-thread access.