[Android] Fix SetSemanticFocus

[rachelkang]

Description of Change

Fixes SetSemanticFocus for Android

Addresses half of #3472

PR Checklist

• Targets the correct branch
• Tests are passing (or failures are unrelated)
• Targets a single property for a single control (or intertwined few properties)
• Adds the property to the appropriate interface
• Avoids any changes not essential to the handler property
• Adds the mapping to the PropertyMapper in the handler
• Adds the mapping method to the WinUI, Android, iOS, and Standard aspects of the handler
• Implements the actual property updates (usually in extension methods in the Platform section of Core)
• Tags ported renderer methods with [PortHandler]
• Adds an example of the property to the sample project (MainPage)
• Adds the property to the stub class
• Implements basic property tests in DeviceTests

Does this PR touch anything that might affect accessibility?

Yes, for the better!

If any of the above checkboxes apply to your PR, then the PR will need to provide testing to demonstrate that accessibility still works.

[jsuarezruiz]

/azp run

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