[Feature] Ability to interact with GridView elements

[jamesmcroft]

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Describe the feature and how it will be used

Introduce the ability to interact with the Uno Platform GridView element.

There should be properties for retrieving the items, the selected item, as well as an action for selecting a specific item by its name.

Platforms

• [x] iOS
• [x] Android
• [x] WebAssembly