Add support for Tizen

[trungnt2910]

Code for Tizen has already been added in the unsupported-platforms branch.

However, this code has not been tested. We will need to:

• Set up the Tizen.NET SDK.
• Build the sample app here, and potentially update any Uno.UI dependencies to fix bugs.
• Copy the Tizen platform code to your local branch and open a pull request to master. Please report any issues or success, with screenshots in the pull request.