Remove IsElementStale method and use existing WebDriverExtensions.IsStale

[Copilot]

Remove IsElementStale method and use existing WebDriverExtensions.IsStale

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Address review feedback from #64542

Description

Removes duplicate IsElementStale methods and updates tests to use the existing IsStale extension method from WebDriverExtensions.cs.

• Removed EnhancedNavigationTestUtil.IsElementStale() (duplicate of WebDriverExtensions.IsStale())
• Removed unused private IsElementStale method from EnhancedNavigationTest.cs
• Updated CanPerformNavigateToFromInteractiveEventHandler test to use originalNavElem.IsStale() extension method

// Before
Assert.Equal(shouldPreserveElements, !EnhancedNavigationTestUtil.IsElementStale(originalNavElem));

// After
Assert.Equal(shouldPreserveElements, !originalNavElem.IsStale());

Addresses feedback from #64542 (comment)

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[ilonatommy]

@copilot, remove also the private IsElementStale from src/Components/test/E2ETest/ServerRenderingTests/EnhancedNavigationTest.cs

[Copilot]

@copilot, remove also the private IsElementStale from src/Components/test/E2ETest/ServerRenderingTests/EnhancedNavigationTest.cs

Removed in 50d23df.