[Feature] Ability to interact with PasswordBox elements

[jamesmcroft]

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Describe the feature and how it will be used

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

There should be properties for interacting with the reveal password button, getting the value, as well as actions for setting the value, appending to the value, and clearing the value.

Recommended to build this on top of the TextBox element.

Platforms

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