Implemented LineHeight on Label

[AmrAlSayed0]

Description of Change

Implements #368 (Re-do of #511)

Additions made

• Adds double LineHeight { get; } to the ILabel interface
• Adds LineHeight property map to LabelHandler
• Adds LineHeight mapping methods to LabelHandler for Android and iOS
• Adds extension methods to apply LineHeight on Android/iOS
• Adds DeviceTests for initial LineHeight values on iOS and 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

[AmrAlSayed0]

@jsuarezruiz My pull request came at an unfortunate time just before a huge commit that made a lot of changes. I re-did the pull request and closed the original one.

[AmrAlSayed0]

@hartez Sorry about the mistake here 😅. I was working blind in VS with no IntelliSense. You can add mutableParagraphStyle.SetParagraphStyle(attribute) right after this line so it copies whatever paragraph style was already there instead of overriding it with the default.