Implement CharacterSpacing property in EntryHandlers

[almirvuk]

Description of Change

Implement CharacterSpacing property in EntryHandlers.

Related issue #382

Platforms Affected

• Core
• iOS
• Android

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 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

[jsuarezruiz]

We would still need to port code related to the Placeholder, could you add a comment here?

[PortHandler ("Partially ported ...")]

[almirvuk]

Done! :)

[mattleibow]

Maybe that needs to be done in this PR? The Placeholder property is already in the new handlers, so I think for this feature to be implemented completely, it needs to update the placeholder as well. Unless there is some specific reason why it can't be done now?

[almirvuk]

From my side it makes sense also, I can do it in this PR :)

[almirvuk]

@mattleibow since this was merged by hartez I will finish the Placeholder part in another PR :)

[hartez]

/azp run

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